usb: gadget: uvc: Add fix for UVC compliance test suite assertion 6.3.90 failure

As per UVC compliance test specification's assertion number 6.3.90
related to 'Standard VS Isochronous Video Data Endpoint Descriptor Assertions',
the bits D3..2 of 'bmAttributes' field of Standard VS Isochronous Video Data
Endpoint Descriptor should be 01 (binary) to indicate that the
synchronization type is ASYNCHRONOUS.

This mandatory requirement has been captured in section 3.10.1.1 of the UVC
Video Class Specification version 1.1

This patch adds a fix for the same.

Signed-off-by: Bhupesh Sharma <bhupesh.sharma@st.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Bhupesh Sharma <bhupesh.sharma@st.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>