io_uring: Fix uninitialized variable up.resv

The variable up.resv is not initialized and is being checking for a
non-zero value in the call to _io_register_rsrc_update. Fix this by
explicitly setting the variable to 0.

Addresses-Coverity: ("Uninitialized scalar variable)"
Fixes: c3bdad02 ("io_uring: add generic rsrc update with tags")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210426094735.8320-1-colin.king@canonical.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -5842,6 +5842,7 @@ static int io_files_update(struct io_kiocb *req, unsigned int issue_flags)
 	up.data = req->rsrc_update.arg;
 	up.nr = 0;
 	up.tags = 0;
+	up.resv = 0;
 
 	mutex_lock(&ctx->uring_lock);
 	ret = __io_register_rsrc_update(ctx, IORING_RSRC_FILE,