selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

The struct adjtimex freq field takes a signed value who's units are in
shifted (<<16) parts-per-million.

Unfortunately for negative adjustments, the straightforward use of:

  freq = ppm << 16 trips undefined behavior warnings with clang:

valid-adjtimex.c:66:6: warning: shifting a negative signed value is undefined [-Wshift-negative-value]
        -499<<16,
        ~~~~^
valid-adjtimex.c:67:6: warning: shifting a negative signed value is undefined [-Wshift-negative-value]
        -450<<16,
        ~~~~^
..

Fix it by using a multiply by (1 << 16) instead of shifting negative values
in the valid-adjtimex test case. Align the values for better readability.

Reported-by: Lee Jones <joneslee@google.com>
Reported-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Link: https://lore.kernel.org/r/20240409202222.2830476-1-jstultz@google.com
Link: https://lore.kernel.org/lkml/0c6d4f0d-2064-4444-986b-1d1ed782135f@collabora.com/

tools/testing/selftests/timers/valid-adjtimex.c

@@ -21,9 +21,6 @@
  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *   GNU General Public License for more details.
  */
-
-
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
@@ -62,45 +59,47 @@ int clear_time_state(void)
 #define NUM_FREQ_OUTOFRANGE 4
 #define NUM_FREQ_INVALID 2
 
+#define SHIFTED_PPM (1 << 16)
+
 long valid_freq[NUM_FREQ_VALID] = {
-	-499<<16,
-	-450<<16,
-	-400<<16,
-	-350<<16,
-	-300<<16,
-	-250<<16,
-	-200<<16,
-	-150<<16,
-	-100<<16,
-	-75<<16,
-	-50<<16,
-	-25<<16,
-	-10<<16,
-	-5<<16,
-	-1<<16,
+	 -499 * SHIFTED_PPM,
+	 -450 * SHIFTED_PPM,
+	 -400 * SHIFTED_PPM,
+	 -350 * SHIFTED_PPM,
+	 -300 * SHIFTED_PPM,
+	 -250 * SHIFTED_PPM,
+	 -200 * SHIFTED_PPM,
+	 -150 * SHIFTED_PPM,
+	 -100 * SHIFTED_PPM,
+	  -75 * SHIFTED_PPM,
+	  -50 * SHIFTED_PPM,
+	  -25 * SHIFTED_PPM,
+	  -10 * SHIFTED_PPM,
+	   -5 * SHIFTED_PPM,
+	   -1 * SHIFTED_PPM,
 	-1000,
-	1<<16,
-	5<<16,
-	10<<16,
-	25<<16,
-	50<<16,
-	75<<16,
-	100<<16,
-	150<<16,
-	200<<16,
-	250<<16,
-	300<<16,
-	350<<16,
-	400<<16,
-	450<<16,
-	499<<16,
+	    1 * SHIFTED_PPM,
+	    5 * SHIFTED_PPM,
+	   10 * SHIFTED_PPM,
+	   25 * SHIFTED_PPM,
+	   50 * SHIFTED_PPM,
+	   75 * SHIFTED_PPM,
+	  100 * SHIFTED_PPM,
+	  150 * SHIFTED_PPM,
+	  200 * SHIFTED_PPM,
+	  250 * SHIFTED_PPM,
+	  300 * SHIFTED_PPM,
+	  350 * SHIFTED_PPM,
+	  400 * SHIFTED_PPM,
+	  450 * SHIFTED_PPM,
+	  499 * SHIFTED_PPM,
 };
 
 long outofrange_freq[NUM_FREQ_OUTOFRANGE] = {
-	-1000<<16,
-	-550<<16,
-	550<<16,
-	1000<<16,
+	-1000 * SHIFTED_PPM,
+	 -550 * SHIFTED_PPM,
+	  550 * SHIFTED_PPM,
+	 1000 * SHIFTED_PPM,
 };
 
 #define LONG_MAX (~0UL>>1)