avcodec/libvpxenc.c: Fix linking with codec interface with msvc.

Default libvpx msvc buils used module definition to export symbols.
These symbols are exported as pointers to data which dont link when
referenced directly.
Reviewed-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/libvpxenc.c

@@ -855,7 +855,7 @@ static const AVCodecDefault defaults[] = {
 #if CONFIG_LIBVPX_VP8_ENCODER
 static av_cold int vp8_init(AVCodecContext *avctx)
 {
-    return vpx_init(avctx, &vpx_codec_vp8_cx_algo);
+    return vpx_init(avctx, vpx_codec_vp8_cx());
 }
 
 static const AVClass class_vp8 = {
@@ -884,7 +884,7 @@ AVCodec ff_libvpx_vp8_encoder = {
 #if CONFIG_LIBVPX_VP9_ENCODER
 static av_cold int vp9_init(AVCodecContext *avctx)
 {
-    return vpx_init(avctx, &vpx_codec_vp9_cx_algo);
+    return vpx_init(avctx, vpx_codec_vp9_cx());
 }
 
 static const AVClass class_vp9 = {