pata_legacy: bogus clock in opti82c46x_set_piomode()

"sysclk" is used as an index into a 4 element array.  My static
checker complains because it can be out of bounds.  From the
context, it looks like there is a right bit shift missing.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>