configure: select vp9_superframe_split_bsf when enabling vp9_decoder

This is required since a5679933c1

Signed-off-by: James Almer <jamrial@gmail.com>

configure

@@ -2637,7 +2637,7 @@ vp6a_decoder_select="vp6_decoder"
 vp6f_decoder_select="vp6_decoder"
 vp7_decoder_select="h264pred videodsp vp8dsp"
 vp8_decoder_select="h264pred videodsp vp8dsp"
-vp9_decoder_select="videodsp vp9_parser"
+vp9_decoder_select="videodsp vp9_parser vp9_superframe_split_bsf"
 webp_decoder_select="vp8_decoder exif"
 wmalossless_decoder_select="llauddsp"
 wmapro_decoder_select="mdct sinewin wma_freqs"