libata-sff: remove harmful BUG_ON from ata_bmdma_qc_issue

libata-sff: remove harmful BUG_ON from ata_bmdma_qc_issue

commit 55ee67f837882f28a900705a2ca1af257ab6c53d upstream.

Remove harmful BUG_ON() from ata_bmdma_qc_issue(),
as it casts too wide of a net and breaks sata_mv.
It also crashes the kernel while doing the BUG_ON().

There's already a WARN_ON_ONCE() further down to catch
the case of POLLING for a BMDMA operation.

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>