mkswap: remove unused variable when compile without libblkid

Signed-off-by: Karel Zak <kzak@redhat.com>
diff --git a/disk-utils/mkswap.c b/disk-utils/mkswap.c
index add732a..27374fd 100644
--- a/disk-utils/mkswap.c
+++ b/disk-utils/mkswap.c
@@ -360,10 +360,9 @@
 	int zap = 1;
 #ifdef HAVE_LIBBLKID
 	blkid_probe pr = NULL;
+	const char *v = NULL;
 #endif
 	if (!ctl->force) {
-		const char *v = NULL;
-
 		if (lseek(ctl->fd, 0, SEEK_SET) != 0)
 			errx(EXIT_FAILURE, _("unable to rewind swap-device"));