ASoC: imx-sgtl5000: Fix uninitialized pointer use in error path

This patch avoids to dereference the uninitialized data pointer if the
error path is entered before devm_kzalloc is called (or if the allocation
fails). It fixes the following warning:

    sound/soc/fsl/imx-sgtl5000.c: In function 'imx_sgtl5000_probe':
    sound/soc/fsl/imx-sgtl5000.c:175:18: warning: 'data' may be used uninitialized in this function [-Wmaybe-uninitialized]

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Mark Brown <broonie@linaro.org>