doc-rst: linux_tv: Fix remaining undefined references

Fix Sphinx those warnings:
	WARNING: undefined label: fdl-modified>`as given on the :ref:`title page <fdl-title-page (if the link has no caption the label must precede a section header)
	WARNING: undefined label: v4l2-pix-fmt-yuv420 (if the link has no caption the label must precede a section $
	WARNING: undefined label: pixfmt-srggb10 (if the link has no caption the label must precede a section heade$
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/linux_tv/media/v4l/fdl-appendix.rst

@@ -246,7 +246,7 @@ Modified Version:
 
    Preserve the section entitled “History”, and its title, and add to it
    an item stating at least the title, year, new authors, and publisher
-   of the :ref:`Modified Version <fdl-modified>`as given on the
+   of the :ref:`Modified Version <fdl-modified>` as given on the
    :ref:`Title Page <fdl-title-page>`. If there is no section entitled
    “History” in the :ref:`Document <fdl-document>`, create one stating
    the title, year, authors, and publisher of the Document as given on

Documentation/linux_tv/media/v4l/pixfmt-srggb10dpcm8.rst

@@ -21,7 +21,7 @@ These four pixel formats are raw sRGB / Bayer formats with 10 bits per
 colour compressed to 8 bits each, using DPCM compression. DPCM,
 differential pulse-code modulation, is lossy. Each colour component
 consumes 8 bits of memory. In other respects this format is similar to
-:ref:`pixfmt-srggb10`.
+:ref:`V4L2-PIX-FMT-SRGGB10`.
 
 
 .. ------------------------------------------------------------------------------

Documentation/linux_tv/media/v4l/pixfmt-yuv420.rst

 .. -*- coding: utf-8; mode: rst -*-
 
 .. _V4L2-PIX-FMT-YVU420:
+.. _V4L2-PIX-FMT-YUV420:
 
 **********************************************************
 V4L2_PIX_FMT_YVU420 ('YV12'), V4L2_PIX_FMT_YUV420 ('YU12')