During hotplug, it is possible for 6Gbps link speed to be limited all
the way down to 1.5 Gbps which may lead to a slower link speed when
drive is re-connected.

This behavior has been seen on a Intel Lewisburg SATA controller
(8086:a1d2) with HGST HUH728080ALE600 drive where SATA link speed was
limited to 1.5 Gbps and when re-connected the link came up 3.0 Gbps.

This patch was retested on above configuration and showed the
hotplugged link to come back online at max speed (6Gbps). I did not
see the downgrade when testing on Intel C600/X79, but retested patched
linux-4.14-rc5 kernel and didn't see any side effects from this
change. Also, successfully retested hotplug on port multiplier 3Gbps
link.

tj: Minor comment updates.

Signed-off-by: David Milburn <dmilburn@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>