io_uring/rsrc: simplify single file node switching

At maximum io_install_fixed_file() removes only one file, so no need to
keep needs_switch state and we can call io_rsrc_node_switch() right after
removal.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/37cfb46f46160f81dced79f646e97db608994574.1681395792.git.asml.silence@gmail.com


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