libspeexenc: use AVSampleFormat instead of deprecated/removed SampleFormat

Fixes build with --enable-libspeex

libavcodec/libspeexenc.c

@@ -319,7 +319,7 @@ AVCodec ff_libspeex_encoder = {
     .encode         = encode_frame,
     .close          = encode_close,
     .capabilities   = CODEC_CAP_DELAY,
-    .sample_fmts    = (const enum SampleFormat[]){ AV_SAMPLE_FMT_S16, AV_SAMPLE_FMT_NONE },
+    .sample_fmts    = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_S16, AV_SAMPLE_FMT_NONE },
     .long_name      = NULL_IF_CONFIG_SMALL("libspeex Speex"),
     .priv_class     = &class,
     .defaults       = defaults,