mpeg2enc: Silence compiler warning
mpeg2enc: Silence compiler warning

Signed-off-by: Xiang, Haihao <8d677183e5993577d4fa73a419b76987913292d6@intel.com>

halleyzhao/libva-fdo,halleyzhao/libva-fdo,CyanogenMod/android_hardware_intel_libva,CyanogenMod/android_hardware_intel_libva,android-ia/hardware_intel_libva,CyanogenMod/android_hardware_intel_libva,android-ia/hardware_intel_libva,halleyzhao/libva-fdo,android-ia/hardware_intel_libva