io_uring: remove unneeded variable 'ret'

Fix the following coccicheck warning:
./fs/io_uring.c:8984:5-8: Unneeded variable: "ret". Return "0" on line
8998

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Link: https://lore.kernel.org/r/1615271441-33649-1-git-send-email-yang.lee@linux.alibaba.com


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