mfd: wm8994-core: Don't use managed regulator bulk get API

The kernel WARNs and then crashes today if wm8994_device_init() fails
after calling devm_regulator_bulk_get().

That happens because there are multiple devices involved here and the
order in which managed resources are freed isn't correct.

The regulators are added as children of wm8994->dev.  Whereas,
devm_regulator_bulk_get() receives wm8994->dev as the device, though it
gets the same regulators which were added as children of wm8994->dev
earlier.

During failures, the children are removed first and the core eventually
calls regulator_unregister() for them. As regulator_put() was never done
for them (opposite of devm_regulator_bulk_get()), the kernel WARNs at

	WARN_ON(rdev->open_count);

And eventually it crashes from debugfs_remove_recursive().

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 wm8994 3-001a: Device is not a WM8994, ID is 0
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 WARNING: CPU: 0 PID: 1 at /mnt/ssd/all/work/repos/devel/linux/driver...