ASoC: dapm: Fix possible uninitialized variable in snd_soc_dapm_get_volsw()

BugLink: http://bugs.launchpad.net/bugs/1638267

commit 01ad5e7d upstream.

If soc_dapm_read() fails, val will be uninitialized, and bogus values
will be written later:

	ret = soc_dapm_read(dapm, reg, &val);
	val = (val >> shift) & mask;

However, the compiler does not give a warning. Return on error before
val is really used to avoid this.

This is similar to the commit 69128316 ("ASoC: dapm: Fix
uninitialized variable in snd_soc_dapm_get_enum_double()")

Fixes: ce0fc93a (ASoC: Add DAPM support at the component level)
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

sound/soc/soc-dapm.c

@@ -3015,6 +3015,9 @@ int snd_soc_dapm_get_volsw(struct snd_kcontrol *kcontrol,
 	}
 	mutex_unlock(&card->dapm_mutex);
 
+	if (ret)
+		return ret;
+
 	if (invert)
 		ucontrol->value.integer.value[0] = max - val;
 	else