usb: pd: release SS lane only if USB host is started

Now that we check for the "USB Communications Capable" bit in
either the Source Capabilities message (in sink mode) or Request
(in source mode), USB host mode is sometimes not even started.
In case DP driver requests to release SS lanes, there is no need
to restart USB host in this case, so add a check for that,
otherwise an error value will be returned which could be
interpreted as a failure to release the SS lanes.

Change-Id: I0e2f9df5f93677692e05713335fc7ba178d20b87
Signed-off-by: Jack Pham <jackp@codeaurora.org>