mc13783-regulator: fix a memory leak in mc13783_regulator_remove

This patch fixes a memory leak by freeing priv in mc13783_regulator_remove

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Liam Girdwood <lrg@slimlogic.co.uk>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>