fs: Fix rw_hint validation

Reject values that are valid rw_hints after truncation but not before
truncation by passing an untruncated value to rw_hint_valid().

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 5657cb07

 ("fs/fcntl: use copy_to/from_user() for u64 types")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20240202203926.2478590-2-bvanassche@acm.org
Signed-off-by: Christian Brauner <brauner@kernel.org>