Platform: OLPC: Fix memleak in olpc_ec_probe

When devm_regulator_register() fails, ec should be
freed just like when olpc_ec_cmd() fails.

Fixes: 231c0c21 ("Platform: OLPC: Add a regulator for the DCON")
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>