usb: dwc3: core: fix order of PM runtime calls

Currently, we disable pm_runtime before all register
accesses are done, this is dangerous and might lead
to abort exceptions due to the driver trying to access
a register which is clocked by a clock which was long
gated.

Fix that by moving pm_runtime_put_sync() and pm_runtime_disable()
as the last thing we do before returning from our ->remove()
method.

Fixes: 72246da4

 (usb: Introduce DesignWare USB3 DRD Driver)
Cc: <stable@vger.kernel.org> # v3.2+
Signed-off-by: Felipe Balbi <balbi@ti.com>