musb: Export musb_root_disconnect for use in modules

Export musb_root_disconnect for use in modules, so that musb glue
code build as module can use it.

This fixes the buildbot errors for -next in arm64-allmodconfig
and arm-allmodconfig.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Fixes: 7cba17ec ("musb: sunxi: Add support for platform_set_mode")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/musb/musb_virthub.c

@@ -245,6 +245,7 @@ void musb_root_disconnect(struct musb *musb)
 			usb_otg_state_string(musb->xceiv->otg->state));
 	}
 }
+EXPORT_SYMBOL_GPL(musb_root_disconnect);
 
 
 /*---------------------------------------------------------------------*/