mfd: wm8994-core: Fix error path in wm8994_device_init

For some errors, the wm8994_device_init function was returning or
jumping to the wrong point in the error path.

Signed-off-by: Anthony Brandon <anthony@amarulasolutions.com>
Reviewed-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>