drivers: ata: pata_arasan_cf: use the same name for the same lock

Note that `&acdev->host->lock' and `qc->ap->lock' denote the same lock, and it's
particularly confusing to spin_lock on the former but spin_unlock on the latter.

Signed-off-by: Iago Abal <mail@iagoabal.eu>
Signed-off-by: Tejun Heo <tj@kernel.org>