USB: pxa27x_udc - Fix Oops

udc_disable oopses dereferencing udc_command.
Signed-off-by: Karl Beldan <karl.beldan@gmail.com>
Acked-by: Robert Jarzmik <rjarzmik@free.fr>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/pxa27x_udc.c

@@ -1526,7 +1526,8 @@ static void udc_disable(struct pxa_udc *udc)
 
 	ep0_idle(udc);
 	udc->gadget.speed = USB_SPEED_UNKNOWN;
-	udc->mach->udc_command(PXA2XX_UDC_CMD_DISCONNECT);
+	if (udc->mach->udc_command)
+		udc->mach->udc_command(PXA2XX_UDC_CMD_DISCONNECT);
 }
 
 /**