io_uring: refactor __io_sqe_files_scm

__io_sqe_files_scm() is now called only from one place passing a single
file, so nr argument can be killed and __io_sqe_files_scm() simplified.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/66b492bc66dc8356d45d64076bb31d677d11a7c9.1649334991.git.asml.silence@gmail.com


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