EncoderConfigAV1: Fix GetMaxBFrameCount

To support driver which does not support B Frame,
GetMaxBFrameCount has been introduced in
#103
but AV1 was not supported yet.

Signed-off-by: Stéphane Cerveau <scerveau@igalia.com>

Author: dabrain34

vk_video_encoder/libs/VkVideoEncoder/VkEncoderConfigAV1.h

@@ -117,6 +117,8 @@ struct EncoderConfigAV1 : public EncoderConfig {
 
     virtual bool InitRateControl() override;
 
+    virtual uint8_t GetMaxBFrameCount() { return  static_cast<uint8_t>(av1EncodeCapabilities.maxBidirectionalCompoundReferenceCount); }
+
     bool GetRateControlParameters(VkVideoEncodeRateControlInfoKHR* rcInfo,
                                   VkVideoEncodeRateControlLayerInfoKHR* rcLayerInfo,
                                   VkVideoEncodeAV1RateControlInfoKHR* rcInfoAV1,