ahci: Remove jmicron fixup

The AHCI set up is handled properly along with the other bits in the
JMICRON quirk. Remove the code whacking it in ahci.c as its un-needed and
also blindly fiddles with bits it doesn't own.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>