media: v4l2-tpg-core.c: fix typo in bt2020_full matrix

My eye fell on this wrong coefficient in the bt2020_full matrix.
The bt2020 matrix (limited range) is OK.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>