Add uninitialized_var() to silence bogus compiler warnings

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/io_u.c b/io_u.c
index 0d24b18..1dff88f 100644
--- a/io_u.c
+++ b/io_u.c
@@ -235,7 +235,7 @@
 static unsigned int get_next_buflen(struct thread_data *td, struct io_u *io_u)
 {
 	const int ddir = io_u->ddir;
-	unsigned int buflen = buflen; /* silence dumb gcc warning */
+	unsigned int uninitialized_var(buflen);
 	unsigned int minbs, maxbs;
 	long r;