avfilter/af_amerge: increase max number of channels from 32 to 64

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/af_amerge.c

@@ -32,7 +32,7 @@
 #include "bufferqueue.h"
 #include "internal.h"
 
-#define SWR_CH_MAX 32
+#define SWR_CH_MAX 64
 
 typedef struct {
     const AVClass *class;