regulator: handle kcalloc() failure

Return -ENOMEM if kcalloc() fails

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>