USB: uvc_v4l2: cleanup test for end of loop

We're trying to test for the the end of the loop here.  "format" is
never NULL.  We don't know what "format->fcc" is because we're past the
end of the loop and I think "fmt->fmt.pix.pixelformat" comes from the
user so we don't know what that is either.  It works, but it's cleaner
to just test to see if (i == ARRAY_SIZE(uvc_formats).

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>