blktrace: Use the new blk_opf_t type

Improve static type checking by using the new blk_opf_t type for a function
argument that represents a combination of a request operation and request
flags. Rename that argument from 'op' into 'opf' to make its role more
clear.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220714180729.1065367-12-bvanassche@acm.org


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