nvenc: Add default value for AVCodecContext::refs

AVCodecContext::refs is used to control the DPB size to be used by the
encoder. The default value for AVCodecContext::refs as set in
libavcodec/options_table.h is 1.

This patch sets AVCodecContext::refs to 0 for h264_nvenc and hevc_nvenc in
order to let the driver take the decision of the correct DPB size to use in
all cases.
Signed-off-by: Srinath K R <skr@nvidia.com>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavcodec/nvenc_h264.c

@@ -109,6 +109,7 @@ static const AVCodecDefault defaults[] = {
     { "qdiff", "-1" },
     { "qblur", "-1" },
     { "qcomp", "-1" },
+    { "refs", "0" },
     { NULL },
 };
 

libavcodec/nvenc_hevc.c

@@ -107,6 +107,7 @@ static const AVCodecDefault defaults[] = {
     { "qdiff", "-1" },
     { "qblur", "-1" },
     { "qcomp", "-1" },
+    { "refs", "0" },
     { NULL },
 };