sata_via: explain the magic fix

Add Joseph Chan's explanation of the problem and workaround to the
VT6421 magic fix.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Joseph Chan <JosephChan@via.com.tw>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
1 file changed