regulator: MAX8997: Fix for divide by zero error

Currently, ramp_delay variable is used uninitialzed in
max8997_set_voltage_ldobuck which gets called through
regulator_register calls.

To fix the problem, in max8997_pmic_probe, ramp_delay initialization
code is moved before calls to regulator_register.

Cc: Liam Girdwood <lrg@ti.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>