usb: dwc3: gadget: END_TRANSFER before CLEAR_STALL command

According the programming guide (for all DWC3 IPs), when the driver
handles ClearFeature(halt) request, it should issue CLEAR_STALL command
_after_ the END_TRANSFER command completes. The END_TRANSFER command may
take some time to complete. So, delay the ClearFeature(halt) request
control status stage and wait for END_TRANSFER command completion
interrupt. Only after END_TRANSFER command completes that the driver
may issue CLEAR_STALL command.

Cc: stable@vger.kernel.org
Fixes: cb11ea56 ("usb: dwc3: gadget: Properly handle ClearFeature(halt)")
Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>