v4l2: Allow ioctl type of "U" for video devices like usb camera

When uvc_gadget application tries to call ioctl to send response for
usb control request, it might call compat_ioctl on platforms having
32bit userspace and 64bit kernel space. This leads to UVC functionality
failure as v4l2_compat_ioctl32() is checking only for ioctl type as "V"
and returning error for usb ioctl of type "U". Hence fix the issue by
adding check for ioctl type of "U" as well and allow calling corresponding
ioctl callback.

Change-Id: I05dbb9d93b85a6a9a547e1280b20dca6a995b64b
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>