usb: dwc2: host: Protect PCGCTL with lock in dwc2_port_resume()

From code inspection, it appears to be unsafe to do a read-modify-write
of PCGCTL in dwc2_port_resume().  Let's make sure the spinlock is held
around this operation.

Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>