usb: dwc3-msm: Unregister bus client upon removal

If probe fails or the platform device is removed, make sure
to unregister the msm_bus_scale client. Otherwise it could
cause the bus driver to access a dangling pointer.

Change-Id: I9eec53d5104cf72c9fdc731cf1bbb5062fe5beb7
Signed-off-by: Jack Pham <jackp@codeaurora.org>