uboot-phytec

power: fix: Do not execute pmic command when not all necessary parameters are passed

Lack of this check resulted in a data abort when CPU tried to execute the
following command (without further mandatory input): 'pmic MAX77686_PMIC'.

Only the 'pmic list' command requires one passed parameter.
Other require at least two valid parameters for correct operation.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>