LoongArch: save one instruction for arch_local_irq_{enable,disable}

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6BWFP

--------------------------------
Signed-off-by: NHongchen Zhang <zhanghongchen@loongson.cn>
Change-Id: I607e48f5abea1184b22326e772d809f6994603cc
(cherry picked from commit f5069ef5)

arch/loongarch/include/asm/irqflags.h

@@ -17,16 +17,15 @@ static inline void arch_local_irq_enable(void)
 	__asm__ __volatile__(
 		"csrxchg %[val], %[mask], %[reg]\n\t"
 		: [val] "+r" (flags)
-		: [mask] "r" (CSR_CRMD_IE), [reg] "i" (LOONGARCH_CSR_CRMD)
+		: [mask] "r" (flags), [reg] "i" (LOONGARCH_CSR_CRMD)
 		: "memory");
 }
 
 static inline void arch_local_irq_disable(void)
 {
-	u32 flags = 0;
 	__asm__ __volatile__(
-		"csrxchg %[val], %[mask], %[reg]\n\t"
-		: [val] "+r" (flags)
+		"csrxchg $zero, %[mask], %[reg]\n\t"
+		:
 		: [mask] "r" (CSR_CRMD_IE), [reg] "i" (LOONGARCH_CSR_CRMD)
 		: "memory");
 }