get_bits: remove unused assignment

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
vp9: remove unused assignment

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Reviewed-by: BBB
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>