powerpc/sparse: Constify the address pointer in __get_user_check()

In __get_user_check, we create an intermediate pointer for the
user address we're about to fetch. We currently don't tag this
pointer as const. Make it const, as we are simply dereferencing
it, and it's scope is limited to the __get_user_check macro.
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/uaccess.h

@@ -274,7 +274,7 @@ do {								\
 ({									\
 	long __gu_err = -EFAULT;					\
 	unsigned long  __gu_val = 0;					\
-	__typeof__(*(ptr)) __user *__gu_addr = (ptr);		\
+	const __typeof__(*(ptr)) __user *__gu_addr = (ptr);		\
 	might_fault();							\
 	if (access_ok(VERIFY_READ, __gu_addr, (size)))			\
 		__get_user_size(__gu_val, __gu_addr, (size), __gu_err);	\