x86/uaccess: Move variable into switch case statement

When building with automatic stack variable initialization, GCC 12
complains about variables defined outside of switch case statements.
Move the variable into the case that uses it, which silences the warning:

./arch/x86/include/asm/uaccess.h:317:23: warning: statement will never be executed [-Wswitch-unreachable]
  317 |         unsigned char x_u8__; \
      |                       ^~~~~~

Fixes: 865c50e ("x86/uaccess: utilize CONFIG_CC_HAS_ASM_GOTO_OUTPUT")
Signed-off-by: Kees Cook <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: kees

arch/x86/include/asm/uaccess.h

@@ -314,11 +314,12 @@ do {									\
 do {									\
 	__chk_user_ptr(ptr);						\
 	switch (size) {							\
-	unsigned char x_u8__;						\
-	case 1:								\
+	case 1:	{							\
+		unsigned char x_u8__;					\
 		__get_user_asm(x_u8__, ptr, "b", "=q", label);		\
 		(x) = x_u8__;						\
 		break;							\
+	}								\
 	case 2:								\
 		__get_user_asm(x, ptr, "w", "=r", label);		\
 		break;							\