[media] vivid-tpg.c: fix wrong Bt.2020 coefficients

Mistyping 0.2627 as 0.2726 I can understand, but -0.4598 as -0.4629? No idea how
I managed that. Anyway, these coefficients are now correct again.

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