[ARM] 3420/1: Missing clobber in example code

Patch from Paul Brook

The example code in the source documentation for __kernel_dmb
clobbers r0 but doesn't list it the asm clobber list.
Signed-off-by: NPaul Brook <paul@codesourcery.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/entry-armv.S

@@ -666,7 +666,7 @@ __kuser_helper_start:
  *
  * #define __kernel_dmb() \
  *         asm volatile ( "mov r0, #0xffff0fff; mov lr, pc; sub pc, r0, #95" \
- *	        : : : "lr","cc" )
+ *	        : : : "r0", "lr","cc" )
  */
 
 __kuser_memory_barrier:				@ 0xffff0fa0