ASoC: fsl_xcvr: check return value after calling platform_get_resource_byname()

It will cause null-ptr-deref if platform_get_resource_byname() returns NULL,
we need check the return value.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20210615013922.784296-10-yangyingliang@huawei.com


Signed-off-by: Mark Brown <broonie@kernel.org>