[PATCH] sil24: add missing ata_pad_free()

sil24_port_stop() is missing call to ata_pad_free() thus leaking pad
buffer when a port is stopped.  This patch adds it.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>