media: videodev2.h.rst.exceptions: add missing exceptions

Add new exceptions for V4L2_COLORSPACE_LAST, V4L2_XFER_FUNC_LAST
and V4L2_YCBCR_ENC_LAST.

This fixes documentation warnings:

Documentation/output/videodev2.h.rst:6: WARNING: undefined label: v4l2-colorspace-last
Documentation/output/videodev2.h.rst:6: WARNING: undefined label: v4l2-xfer-func-last
Documentation/output/videodev2.h.rst:6: WARNING: undefined label: v4l2-ycbcr-enc-last

Signed-off-by: Hans Verkuil <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/userspace-api/media/videodev2.h.rst.exceptions

···
 replace symbol V4L2_COLORSPACE_SMPTE170M :c:type:`v4l2_colorspace`
 replace symbol V4L2_COLORSPACE_SMPTE240M :c:type:`v4l2_colorspace`
 replace symbol V4L2_COLORSPACE_SRGB :c:type:`v4l2_colorspace`
+replace symbol V4L2_COLORSPACE_LAST :c:type:`v4l2_colorspace`
 
 # Documented enum v4l2_xfer_func
 replace symbol V4L2_XFER_FUNC_709 :c:type:`v4l2_xfer_func`
···
 replace symbol V4L2_XFER_FUNC_SMPTE2084 :c:type:`v4l2_xfer_func`
 replace symbol V4L2_XFER_FUNC_SMPTE240M :c:type:`v4l2_xfer_func`
 replace symbol V4L2_XFER_FUNC_SRGB :c:type:`v4l2_xfer_func`
+replace symbol V4L2_XFER_FUNC_LAST :c:type:`v4l2_xfer_func`
 
 # Documented enum v4l2_ycbcr_encoding
 replace symbol V4L2_YCBCR_ENC_601 :c:type:`v4l2_ycbcr_encoding`
···
 replace symbol V4L2_YCBCR_ENC_XV601 :c:type:`v4l2_ycbcr_encoding`
 replace symbol V4L2_YCBCR_ENC_XV709 :c:type:`v4l2_ycbcr_encoding`
 replace symbol V4L2_YCBCR_ENC_SMPTE240M :c:type:`v4l2_ycbcr_encoding`
+replace symbol V4L2_YCBCR_ENC_LAST :c:type:`v4l2_ycbcr_encoding`
 
 # Documented enum v4l2_hsv_encoding
 replace symbol V4L2_HSV_ENC_180 :c:type:`v4l2_hsv_encoding`