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

This patch does not change any functionality.

Cc: Omar Sandoval <osandov@fb.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220714180729.1065367-10-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>