sata_via: apply magic FIFO fix to vt6420 too

sata_via: apply magic FIFO fix to vt6420 too

commit b1353e4f40f6179ab26a3bb1b2e1fe29ffe534f5 upstream.

vt6420 has the same FIFO overflow problem as vt6421 when combined with
certain devices.  This patch applies the magic fix to vt6420 too.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Martin Qvist <q@maq.dk>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Cc: Joseph Chan <JosephChan@via.com.tw>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>