usb: dwc3: Do pm_runtime_disable after removing children

When trying to remove the child, device core is trying to resume one last
time before unloading. All parents should be in active state before
resuming the child, but since dwc3_msm may be runtime suspended, removal
of child device could result in unclocked register access.
Hence do a pm_runtime_get_sync prior to removing children to ensure parent
is in active state. However sometimes pm_runtime_get_sync fails in case of
system suspend. In this case turn on the clocks manually.

CRs-fixed: 682513
Change-Id: I3b25a8d96a2efedd0235a53683fcb4d8659bc54f
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>