wcd9335: fix a incorrect use of kstrndup()

In wcd9335_codec_enable_dec(), 'widget_name' is allocated by kstrndup().
However, according to doc: "Note: Use kmemdup_nul() instead if the size
is known exactly." So we should use kmemdup_nul() here instead of
kstrndup().
Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wcd9335.c

@@ -2734,7 +2734,7 @@ static int wcd9335_codec_enable_dec(struct snd_soc_dapm_widget *w,
 	char *dec;
 	u8 hpf_coff_freq;
 
-	widget_name = kstrndup(w->name, 15, GFP_KERNEL);
+	widget_name = kmemdup_nul(w->name, 15, GFP_KERNEL);
 	if (!widget_name)
 		return -ENOMEM;