QIconvCodec: fix compilation when NO_BOM is defined.

qiconvcodec.cpp:305:34: error: unused parameter 'cd' [-Werror,-Wunused-parameter]

Change-Id: I27eaacb532114dd188c4ffff13d330b64b4feaa6
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/corelib/codecs/qiconvcodec.cpp

@@ -323,6 +323,8 @@ static bool setByteOrder(iconv_t cd)
     if (iconv(cd, inBytesPtr, &inBytesLeft, &outBytes, &outBytesLeft) == (size_t) -1) {
         return false;
     }
+#else
+    Q_UNUSED(cd);
 #endif // NO_BOM
 
     return true;