LoongArch: Simplify __arch_bitrev32() implementation

LoongArch has the bitrev.w instruction to reverse bits in a 32-bit
integer, thus there's no need to reverse the bytes and use bitrev.4b.

Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: xry111

arch/loongarch/include/asm/bitrev.h

@@ -11,7 +11,7 @@ static __always_inline __attribute_const__ u32 __arch_bitrev32(u32 x)
 {
 	u32 ret;
 
-	asm("bitrev.4b	%0, %1" : "=r"(ret) : "r"(__swab32(x)));
+	asm("bitrev.w	%0, %1" : "=r"(ret) : "r"(x));
 	return ret;
 }