[media] ds3000: fix reading array out of bound in ds3000_read_snr

An attempt was made to read dvbs2_snr_tab[80],
though dvbs2_snr_tab has only 80 elements.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>