ASoC: Tegra: wm8903: Remove redundant drvdata clears

When the driver is not initialized/registered, nothing should be touching
these fields anyway, so there's no point clearing them out.

(Applying Mark's TrimSlice review comments to the existing driver)

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>