ARM: Use a definition for the userspace cmpxchg emulation syscall

Use a definition for the cmpxchg SWI instead of hard-coding the number.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 1bbda04..3f361a7 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -528,7 +528,7 @@
 	 * __kuser_cmpxchg code in entry-armv.S should be aware of its
 	 * existence.  Don't ever use this from user code.
 	 */
-	case 0xfff0:
+	case NR(cmpxchg):
 	for (;;) {
 		extern void do_DataAbort(unsigned long addr, unsigned int fsr,
 					 struct pt_regs *regs);