h264,h265parse: Fix coverity issues

h264parse: Remove useless comparison

sei_pic_struct is unsigned and GST_H264_SEI_PIC_STRUCT_FRAME is zero.        
CID: 1461467

h265parser: Fix some coverity issues

- Remove useless comparison
- Fix invalid memory access

CID: 1461477, 1461476, 1461475, 1461474