regulator core: fix double-free in regulator_register() error path

During regulator registration, any error after device_register() will
cause a double-free on the struct regulator_dev 'rdev'.  The bug is in
drivers/regulator/core.c:regulator_register():

...
scrub:
	device_unregister(&rdev->dev);
clean:
	kfree(rdev);                           <---
	rdev = ERR_PTR(ret);
	goto out;
...

device_unregister() calls regulator_dev_release() which frees rdev.  The
subsequent kfree corrupts memory and causes some OMAP3 systems to oops on
boot in regulator_get().

Applies against 2.6.30-rc3.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>