dcadec: replace ldexpf with a multiplication by a constant

Signed-off-by: NAnton Khirnov <anton@khirnov.net>

libavcodec/dcadec.c

@@ -1699,7 +1699,7 @@ static float dca_dmix_code(unsigned code)
 {
     int sign = (code >> 8) - 1;
     code &= 0xff;
-    return ldexpf((dca_dmixtable[code] ^ sign) - sign, -15);
+    return ((dca_dmixtable[code] ^ sign) - sign) * (1.0 / (1U << 15));
 }
 
 /**