dcadec: initialize variables before use

CC: libav-stable@libav.org
Bug-Id: CID 700751 / CID 700752

libavcodec/dcadec.c

@@ -1462,11 +1462,11 @@ static int dca_exss_parse_asset_header(DCAContext *s)
 {
     int header_pos = get_bits_count(&s->gb);
     int header_size;
-    int channels;
+    int channels = 0;
     int embedded_stereo = 0;
     int embedded_6ch    = 0;
     int drc_code_present;
-    int extensions_mask;
+    int extensions_mask = 0;
     int i, j;
 
     if (get_bits_left(&s->gb) < 16)