io_uring: remove redundant assignment to ret in io_register_iowq_max_workers()

io_uring: remove redundant assignment to ret in io_register_iowq_max_workers()

After the assignment, only exit path with label 'err' uses ret as
return value. However,before exiting through this path with label 'err',
ret is assigned with the return value of io_wq_max_workers(). Hence, the
initial assignment is redundant and can be removed.

Signed-off-by: Nghia Le <nghialm78@gmail.com>
Link: https://lore.kernel.org/r/20211102190521.28291-1-nghialm78@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>