ceph: keep consistent semantic in fscache related option combination

When specifying multiple fscache related options, the result isn't always
the same as option order, this fix will keep strict consistent meaning
by order.
Signed-off-by: NChengguang Xu <cgxu519@icloud.com>
Reviewed-by: N"Yan, Zheng" <zyan@redhat.com>
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>

fs/ceph/super.c

@@ -314,9 +314,13 @@ static int parse_fsopt_token(char *c, void *private)
 		break;
 	case Opt_fscache:
 		fsopt->flags |= CEPH_MOUNT_OPT_FSCACHE;
+		kfree(fsopt->fscache_uniq);
+		fsopt->fscache_uniq = NULL;
 		break;
 	case Opt_nofscache:
 		fsopt->flags &= ~CEPH_MOUNT_OPT_FSCACHE;
+		kfree(fsopt->fscache_uniq);
+		fsopt->fscache_uniq = NULL;
 		break;
 	case Opt_poolperm:
 		fsopt->flags &= ~CEPH_MOUNT_OPT_NOPOOLPERM;