avformat/wavenc: Change enum to int, which is accessed via AVOption as int

This fixes depending on implementation defined behavior
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/wavenc.c

@@ -82,7 +82,7 @@ typedef struct WAVMuxContext {
     int write_peak;
     int rf64;
     int peak_block_size;
-    PeakFormat peak_format;
+    int peak_format;
     int peak_block_pos;
     int peak_ppv;
     int peak_bps;