[PATCH] Fix HD activity LED with ahci

Patch: fix wrong HD activity control by ahci driver

The ahci driver 1.0 sets the SActive bit on every transaction,
causing the LED to light up. The SActive bit is used only for
native command queuing (NCQ) which the current driver version
doesn't implement. Resetting the SActive bit is the device's
responsibility (by sending a "Set Device Bits FIS" to the
host adapter) but this is not required in response to
non-NCQ commands, and (most) devices don't. Thus the LED
stays always on. This patch fixes the LED behavior.

Spec references:
http://www.intel.com/technology/serialata/pdf/rev1_1.pdf, sec. 3.3.13, 5.5.1
http://www.serialata.org/docs/serialata10a.pdf
http://www.intel.com/design/storage/papers/25266401.pdf



Signed-off-by:  <Martin.Wilck@fujitsu-siemens.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>