[media] m88ds3103: remove useless most significant bit clear

No need to clear negative msb bits as those were dropped in any
case when data is written to register.

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