lavc/avcodec: Constify the return value of av_bitstream_filter_next().

Fixes the following gcc warning:
libavcodec/bitstream_filter.c:39:12: warning: return discards 'const' qualifier from pointer target type

libavcodec/avcodec.h

@@ -5484,7 +5484,7 @@ void av_bitstream_filter_close(AVBitStreamFilterContext *bsf);
  * filters.
  */
 attribute_deprecated
-AVBitStreamFilter *av_bitstream_filter_next(const AVBitStreamFilter *f);
+const AVBitStreamFilter *av_bitstream_filter_next(const AVBitStreamFilter *f);
 #endif
 
 /**

libavcodec/bitstream_filter.c

@@ -28,7 +28,7 @@
 #if FF_API_OLD_BSF
 FF_DISABLE_DEPRECATION_WARNINGS
 
-AVBitStreamFilter *av_bitstream_filter_next(const AVBitStreamFilter *f)
+const AVBitStreamFilter *av_bitstream_filter_next(const AVBitStreamFilter *f)
 {
     const AVBitStreamFilter *filter = NULL;
     void *opaque = NULL;

libavcodec/version.h

@@ -29,7 +29,7 @@
 
 #define LIBAVCODEC_VERSION_MAJOR  58
 #define LIBAVCODEC_VERSION_MINOR   0
-#define LIBAVCODEC_VERSION_MICRO 100
+#define LIBAVCODEC_VERSION_MICRO 101
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
                                                LIBAVCODEC_VERSION_MINOR, \