codecs: gstvp9statefulparser: feature_data should be 0 if feature_enable is 0

The spec says in 6.2.11 that feature_data[i][j] should be zero if feature_enabled[i][j] is zero. Instead we retained the old value in the parser. Fix it.

Relevant spec excerpt:

feature_enabled equal to 0 indicates that the corresponding feature is unused and has value equal to 0. feature_enabled equal to 1 indicates that the feature value is coded in the bitstream.