io_uring: return REQ_F_ flags from io_file_get_flags

Two of the three callers want them, so return the more usual format,
and shift into the FFS_ form only for the fixed file table.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230620113235.920399-6-hch@lst.de


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