pata-rb532-cf: replace rb532_pata_finish_io()

Since the delay used internally is just the same as ata_sff_pause()
uses, rb532_pata_finish_io() does exactly the same as ata_sff_pause()
and thus can be replaced by the later one.

Signed-off-by: Phil Sutter <n0-1@freewrt.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>