x86: adjust placement of pause insn in _raw_spin_lock()

React to lock becoming available as quickly as possible.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

xen/include/asm-x86/spinlock.h

@@ -23,8 +23,8 @@ static inline void _raw_spin_lock(spinlock_t *lock)
         "1:  lock; decb %0         \n"
         "    js 2f                 \n"
         ".section .text.lock,\"ax\"\n"
-        "2:  cmpb $0,%0            \n"
-        "    rep; nop              \n"
+        "2:  rep; nop              \n"
+        "    cmpb $0,%0            \n"
         "    jle 2b                \n"
         "    jmp 1b                \n"
         ".previous"