[libata] ahci: Withdraw IGN_SERR_INTERNAL for SB800 SATA

There is an issue in ATI SB600/SB700 SATA that PxSERR.E should not be
set on some conditions, which will lead to many SATA ODD error messages.
commit 55a61604 is the workaround.
Since SB800 fixed this HW issue, IGN_SERR_INTERNAL should be withdrawn
for SB800.

Signed-off-by: Shane Huang <shane.huang@amd.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>