avcodec/avcodec: Update check for identical colorspace/primaries/trc names

avcodec/avcodec: Update check for identical colorspace/primaries/trc names

If the numerical constants for colorspace, transfer characteristics
and color primaries coincide, the current code presumes the
corresponding names to be identical and prints only one of them obtained
via av_get_colorspace_name(). There are two issues with this: The first
is that the underlying assumption is wrong: The names only coincide in
the 0-7 range, they differ for more recent additions. The second is that
av_get_colorspace_name() is outdated itself; it has not been updated
with the names of the newly defined colorspaces.

Fix both of this by using the names from
av_color_(space|primaries|transfer)_name() and comparing them via
strcmp; don't use av_get_colorspace_name() at all.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>