dm integrity: fix logic bug in integrity tag testing

If all the bytes are equal to DISCARD_FILLER, we want to accept the
buffer. If any of the bytes are different, we must do thorough
tag-by-tag checking.

The condition was inverted.

Fixes: 84597a44 ("dm integrity: add optional discard support")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-integrity.c

@@ -1333,7 +1333,7 @@ static int dm_integrity_rw_tag(struct dm_integrity_c *ic, unsigned char *tag, se
 			if (likely(is_power_of_2(ic->tag_size))) {
 				if (unlikely(memcmp(dp, tag, to_copy)))
 					if (unlikely(!ic->discard) ||
-					    unlikely(!memchr_inv(dp, DISCARD_FILLER, to_copy))) {
+					    unlikely(memchr_inv(dp, DISCARD_FILLER, to_copy) != NULL)) {
 						goto thorough_test;
 				}
 			} else {