usb: gadget: f_hid: fix: Free out requests

Requests for out endpoint are allocated in bind() function
but never released.

This commit ensures that all pending requests are released
when we disable out endpoint.

Fixes: 99c51500

 ("usb: gadget: hidg: register OUT INT endpoint for SET_REPORT")
Cc: stable@vger.kernel.org
Tested-by: David Lechner <david@lechnology.com>
Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>