vaapih264enc/vaapih264feienc: unused value from coverity scan.

Submitted by wangfei @wangfei

Link to original bug (#797365)

Description

2 place of unused value from coverity scan:

643 seq_param->intra_idr_period = GST_VAAPI_ENCODER_KEYFRAME_PERIOD (feienc);
CID 370611 (#1 (closed) of 1): Unused value (UNUSED_VALUE)
assigned_value: Assigning value from 1U + feienc->num_bframes to seq_param->ip_period here, but that stored value is overwritten before it can be used.
644 seq_param->ip_period = 1 + feienc->num_bframes;
value_overwrite: Overwriting previous write to seq_param->ip_period with value from (seq_param->intra_period > 1U) ? 1U + feienc->num_bframes : 0U.
645 seq_param->ip_period = seq_param->intra_period > 1 ?