io_uring: fix resource leak in io_import_dmabuf()

Replace the return statement with setting ret = -EINVAL and jumping to
the err label to ensure resources are released via io_release_dmabuf.

Fixes: a5c98e94 ("io_uring/zcrx: dmabuf backed zerocopy receive")
Signed-off-by: Penglei Jiang <superman.xpt@gmail.com>
Link: https://lore.kernel.org/r/20250625102703.68336-1-superman.xpt@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>