Fix following IntraPeriod set issue

1. In WelsInitSps function, if kuiIntraPeriod is huge, uiLog2MaxFrameNum might be bigger than 15, which may introduce illegal H264 bitstream. Fix issue #1311.
2. if pSvcParm.uiIntraPeriod is not zero (e.g. 14) at the initial, it will init sps.iLog2MaxPocLsb. to 5.
 But if I changed pSvcParm.uiIntraPeriod to 40, sps.iLog2MaxPocLsb. is still 5, need to recalcuted this parameter.
 (Same with uiLog2MaxFrameNum.)