generate_wave_table: Add include for AVSampleFormat

Fixes warning in `make checkheaders`.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/generate_wave_table.h

@@ -19,6 +19,8 @@
 #ifndef AVFILTER_GENERATE_WAVE_TABLE_H
 #define AVFILTER_GENERATE_WAVE_TABLE_H
 
+#include "libavutil/samplefmt.h"
+
 enum WaveType {
     WAVE_SIN,
     WAVE_TRI,