MIPS: atomic: Use _atomic barriers in atomic_sub_if_positive()

Use smp_mb__before_atomic() & smp_mb__after_atomic() in
atomic_sub_if_positive() rather than the equivalent
smp_mb__before_llsc() & smp_llsc_mb(). The former are more standard &
this preps us for avoiding redundant duplicate barriers on Loongson3 in
a later patch.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org

arch/mips/include/asm/atomic.h

@@ -196,7 +196,7 @@ static __inline__ int atomic_sub_if_positive(int i, atomic_t * v)
 {
 	int result;
 
-	smp_mb__before_llsc();
+	smp_mb__before_atomic();
 
 	if (kernel_uses_llsc) {
 		int temp;
@@ -237,7 +237,7 @@ static __inline__ int atomic_sub_if_positive(int i, atomic_t * v)
 	 * another barrier here.
 	 */
 	if (!__SYNC_loongson3_war)
-		smp_llsc_mb();
+		smp_mb__after_atomic();
 
 	return result;
 }