block/bfq: Use the new blk_opf_t type

Use the new blk_opf_t type for arguments and variables that represent
request flags or a bitwise combination of a request operation and
request flags. Rename those variables from 'op' into 'opf'.

This patch does not change any functionality.

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220714180729.1065367-8-bvanassche@acm.org


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