sata_mv: drop unncessary EH callback resetting

Now that BMDMA EH ops are separated out from SFF ops, mv5_ops doesn't
have to explicitly reset ->error_handler() and ->post_internal_cmd().
Drop them.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>