dca: include libavutil/mathematics.h for possibly missing M_SQRT1_2

Signed-off-by: Janne Grunau <janne-libav@jannau.net>
Signed-off-by: Reinhard Tartler <siretart@tauware.de>

libavcodec/dca.c

@@ -29,6 +29,7 @@
 #include "libavutil/common.h"
 #include "libavutil/intmath.h"
 #include "libavutil/intreadwrite.h"
+#include "libavutil/mathematics.h"
 #include "libavutil/audioconvert.h"
 #include "avcodec.h"
 #include "dsputil.h"