io_uring/region: fix error codes after failed vmap

io_create_region() jumps after a vmap failure without setting the return
code, it could be 0 or just uninitialised.

Fixes: dfbbfbf1 ("io_uring: introduce concept of memory regions")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0abac19dbf81c061cffaa9534a2471ed5460ad3e.1731803848.git.asml.silence@gmail.com


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