avfilter/asubprocess: use little endian sample values for wav data

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

libavfilter/af_asubprocess.c

 #include "libavutil/opt.h"
 #include "libavutil/mem.h"
+#include "libavutil/intreadwrite.h"
 #include "libavformat/avio.h"
 #include "libavformat/avio_internal.h"
 
@@ -303,7 +304,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
     int k = 0;
     int32_t *xd = (int32_t *)in->data[0];
     for (k = 0; k < in->nb_samples * inlink->ch_layout.nb_channels; k++) {
-        buffer[k] = xd[k] >> 16;
+        AV_WL16 (buffer + k, xd[k] >> 16);
     }
     sp_write (s->sp, buffer, 2 * k);
     if (s->eof)
@@ -360,7 +361,8 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
             int32_t *xd = (int32_t *)out->data[0];
             for (int k = 0; k < avail * inlink->ch_layout.nb_channels; k++)
             {
-                xd[k] = buffer[k] << 16;
+                short v = AV_RL16 (buffer + k);
+                xd[k] = v << 16;
             }
             ret = ff_filter_frame(outlink, out);
         }