GFS2: Fix typo

A missing ! in a test.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/sys.c

@@ -233,7 +233,7 @@ static ssize_t demote_rq_store(struct gfs2_sbd *sdp, const char *buf, size_t len
 	glops = gfs2_glops_list[gltype];
 	if (glops == NULL)
 		return -EINVAL;
-	if (test_and_set_bit(SDF_DEMOTE, &sdp->sd_flags))
+	if (!test_and_set_bit(SDF_DEMOTE, &sdp->sd_flags))
 		fs_info(sdp, "demote interface used\n");
 	rv = gfs2_glock_get(sdp, glnum, glops, 0, &gl);
 	if (rv)