media: media.h.rst.exceptions: ignore MEDIA-ENT-F-DTV-DECODER

This was kept just for backward compatibility. Solves this warning:
	media.h.rst:6: WARNING: undefined label: media-ent-f-dtv-decoder (if the link has no caption the label must precede a section header)

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>