sh: cmpxchg: fix a bit shift bug in big_endian os

Correct bitoff in big endian OS.
Current code works correctly for 1 byte but not for 2 bytes.

Fixes: 3226aad81aa6 ("sh: support 1 and 2 byte xchg")
Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rich Felker <dalias@libc.org>
diff --git a/arch/sh/include/asm/cmpxchg-xchg.h b/arch/sh/include/asm/cmpxchg-xchg.h
index 7219719..1e881f5 100644
--- a/arch/sh/include/asm/cmpxchg-xchg.h
+++ b/arch/sh/include/asm/cmpxchg-xchg.h
@@ -21,7 +21,7 @@
 	int off = (unsigned long)ptr % sizeof(u32);
 	volatile u32 *p = ptr - off;
 #ifdef __BIG_ENDIAN
-	int bitoff = (sizeof(u32) - 1 - off) * BITS_PER_BYTE;
+	int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
 #else
 	int bitoff = off * BITS_PER_BYTE;
 #endif