io_uring/rsrc: fix a comment in io_import_fixed()

io_import_fixed() supports offsets, but "may not" means the opposite.
Replace it with "might not" so the comments rather speaks about
possible cases.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Link: https://lore.kernel.org/r/5b5f79958456caa6dc532f6205f75f224b232c81.1676902343.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>