usb: dwc3-msm: Flush bus_vote_w work on pm_suspend and freeze

Currently as a part of dwc3_msm_pm_suspend, driver calls suspend
routine which schedules bus_vote_w to remove bus votes from USB.
But it could be possible that the system freezes before the work
function could get called or completed. This will keep the USB
votes enabled and block XO shutdown.
Fix this by flushing the bus_vote_w at the end of pm_suspend to
ensure that bus votes are removed.

Change-Id: I578e3c4434eb04740f07f4dd0640a945a86fde8b
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>