media: ca-reset.rst: add some description to this ioctl

While we don't have any documentation for it, based on what's
there at Kaffeine and VDR, it seems that this command should
be issued before start using CA. So, document it as such.

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