media: v4l: dvb-frontends: stb0899: fix comparison to bitshift when dealing with a mask

Due to a typo, the mask was destroyed by a comparison instead of a bit
shift.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>