hevcenc: clear BitWriter buffer after using it.
hevcenc: clear BitWriter buffer after using it.

Signed-off-by: Zhong Cong <fbc1588e6b9489a864c9ee5f55f730ef2ee5e810@intel.com>

halleyzhao/libyami,lizhong1008/libyami,uartie/libyami,chivakker/libyami,halleyzhao/libyami,seanvk/libyami,dspmeng/libyami,yizhouwei/libyami,uartie/libyami,zhaobob/libyami,clearlylin/libyami,YuJiankang/libyami,lizhong1008/libyami,clearlylin/libyami,yizhouwei/libyami,zhaobob/libyami,stripes416/libyami,chivakker/libyami,stripes416/libyami,01org/libyami,chivakker/libyami,clearlylin/libyami,seanvk/libyami,halleyzhao/libyami,andyLiuChina/libyami,dspmeng/libyami,seanvk/libyami,BtbN/libyami,01org/libyami,uartie/libyami,zhaobob/libyami,BtbN/libyami,halleyzhao/libyami,BtbN/libyami,BtbN/libyami,YuJiankang/libyami,01org/libyami,andyLiuChina/libyami,andyLiuChina/libyami,andyLiuChina/libyami,stripes416/libyami,YuJiankang/libyami,lizhong1008/libyami,yizhouwei/libyami,dspmeng/libyami