linux-phytec-ti

[media] dvb_ringbuffer.h: document the define macros

There are a few define macros not documented, because the ReST
output was causing more warnings.

Now that this got fixed, document them. While here, fix the
remaining coding style issues.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>