ASoC: wm8958-dsp: Fix firmware block loading

The codec->control_data contains a pointer to the device's regmap struct. But
wm8994_bulk_write() expects a pointer to the parent wm8998 device.

The issue was introduced in commit d9a7666f ("ASoC: Remove ASoC-specific
WM8994 I/O code").

Fixes: d9a7666f ("ASoC: Remove ASoC-specific WM8994 I/O code")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org