[IDE] Use the block layer deferred softirq request completion

This patch makes IDE use the new blk_complete_request() interface.
There's still room for improvement, as __ide_end_request() really
could drop the lock after getting HWGROUP->rq (why does it need to
hold it in the first place? If ->rq access isn't serialized, we are
screwed anyways).

Signed-off-by: Jens Axboe <axboe@suse.de>