sata_sil24: memset() overflow

cb->atapi.cdb is an array of 16 u8 elements.  The call too memset()
would set the first part of the sge array to zero as well.  It's not
a packed struct.

This one has been around for five years.  I found it with Smatch.  I
think the reason no one has seen it before is because we normally call
sil24_fill_sg() and that overwrites sge with proper information?

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>