ASoC: samsung-i2s: Check secondary DAI exists before referencing

ASoC: samsung-i2s: Check secondary DAI exists before referencing

commit 133c2681c4a0c1b589d138c2fdd0f131bdce20ed upstream.

In a couple of places the driver is missing a check to ensure there is a
secondary DAI before it de-references the pointer to it, causing a null
pointer de-reference. This patch adds a check to avoid this.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
[lizf: Backported to 3.4: drop the changes to i2s_shutdown()]
Signed-off-by: Zefan Li <lizefan@huawei.com>