uuid: Take const on input of uuid_is_null() and guid_is_null()

The null check functions do not and must not modify contents of the UUID
or GUID supplied.

Mark argument explicitly to reflect that.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

include/linux/uuid.h

@@ -48,7 +48,7 @@ static inline void guid_copy(guid_t *dst, const guid_t *src)
 	memcpy(dst, src, sizeof(guid_t));
 }
 
-static inline bool guid_is_null(guid_t *guid)
+static inline bool guid_is_null(const guid_t *guid)
 {
 	return guid_equal(guid, &guid_null);
 }
@@ -63,7 +63,7 @@ static inline void uuid_copy(uuid_t *dst, const uuid_t *src)
 	memcpy(dst, src, sizeof(uuid_t));
 }
 
-static inline bool uuid_is_null(uuid_t *uuid)
+static inline bool uuid_is_null(const uuid_t *uuid)
 {
 	return uuid_equal(uuid, &uuid_null);
 }