Doxygen eats the newline in the first comment, making it harder to read.
Join the lines and add a comma, so source and documentation are equally readable.

Doxygen only associates the second comment with cust_dec.
The comments for cust_dec and cust_tab make perfect sense without it,
so downgrade it to a non-doxygen "//" comment.

The third comment was missed by the command in the previous commit,
because it (correctly but uniquely) doesn't have a trailing comma.
Signed-off-by: Andrew Sayers <ffmpeg-devel@pileofstuff.org>