usb: musb: fix device hotplug behind hub

The commit 889ad3b "usb: musb: try a race-free wakeup" breaks device
hotplug enumeraitonn when the device is connected behind a hub while usb
autosuspend is enabled.

Adding finish_resume_work into runtime resume callback fixes the issue.

Also resume root hub is required to resume the bus from runtime suspend,
so move musb_host_resume_root_hub() back to its original location, where
handles RESUME interrupt.

Signed-off-by: Bin Liu <b-liu@ti.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>