MIPS: AR7: allow NULL clock for clk_get_rate

Make the behaviour of clk_get_rate consistent with common clk's
clk_get_rate by accepting NULL clocks as parameter. Some device
drivers rely on this, and will cause an OOPS otherwise.

Fixes: 780019ddf02f ("MIPS: AR7: Implement clock API")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Reported-by: Mathias Kresin <dev@kresin.me>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16775/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/ar7/clock.c

@@ -430,6 +430,9 @@ EXPORT_SYMBOL(clk_disable);
 
 unsigned long clk_get_rate(struct clk *clk)
 {
+	if (!clk)
+		return 0;
+
 	return clk->rate;
 }
 EXPORT_SYMBOL(clk_get_rate);