USB: musb: resume suspended root hub on disconnect

If this is not done, khubd will not be informed of the disconnect
and will assume the device is still there.

Easily seen when a hub is connected with no device attached to it;
it will autosuspend.  When the hub is disconnected, it still shows
up in /proc/bus/usb/devices

Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
Acked-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>