piix_init_one() allocates host private data which should be freed by
piix_host_stop().  ich_pata_ops wasn't converted to piix_host_stop()
while merging, leaking 4 bytes on driver detach.  Fix it.

This was spotted using Kmemleak by Catalin Marinas.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Catalin Marinas <catalin.marinas@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>