Regulator: core: Unregister when gpio request fails.

If the gpio_request_one() fails, or returns EPROBE_DEFER, the
regulator must be device_unregister()ed. When this is not done,
there are WARNING: from sysfs:

WARNING: at fs/sysfs/file.c:343 sysfs_open_file+0x238/0x268()

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>