um: get rid of pointless include "..." where include <...> will do

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/drivers/slip_user.c

@@ -11,10 +11,10 @@
 #include <string.h>
 #include <sys/termios.h>
 #include <sys/wait.h>
-#include "net_user.h"
-#include "os.h"
+#include <net_user.h>
+#include <os.h>
 #include "slip.h"
-#include "um_malloc.h"
+#include <um_malloc.h>
 
 static int slip_user_init(void *data, void *dev)
 {