libs: enc: h265: reset num_ref_idx_l1_active_minus1 when low delay B.
When enable low delay B, the reference list 1 will be same with reference list 0, so need reset the num_ref_idx_l1_active_minus1 to num_ref_idx_l0_active_minus1.
When enable low delay B, the reference list 1 will be same with reference list 0, so need reset the num_ref_idx_l1_active_minus1 to num_ref_idx_l0_active_minus1.