UPSTREAM: io_uring: add missing item types for splice request

Splice is like read/write and should grab current->nsproxy, denoted by
IO_WQ_WORK_FILES as it refers to current->files as well

Change-Id: I94a99fdef5764e7eda5da778b5b52a150b9fe5eb
Signed-off-by: Bing-Jhong Billy Jheng <billy@starlabs.sg>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 75454b4b)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Signed-off-by: Lee Jones <joneslee@google.com>