usb: gadget: dummy_hcd: Fix wrong power status bit clear/reset in dummy_hub_control()

This fixes the commit: 1cd8fd28 ("usb: gadget: dummy_hcd: add
SuperSpeed support").

In the case of ClearPortFeature and USB_PORT_FEAT_POWER, simply clear
the right bit regardless of what the wValue is.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>