usb: musb: fix musb pointer acqusition in musb_host_finish_resume

This is a fall-out from "usb: musb: finish suspend/reset work
independently from musb_hub_control()" that I missed because the
MUSB_POWER register does not have the MUSB_POWER_SUSPENDM bit set on
AM335x platforms; hence the code path was not travelled in my tests.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>