PM / devfreq: rk3399_dmc: Remove explictly regulator_put call in .remove

Current code uses devm_regulator_get() in .probe so a regulator_put() will
be automatically called when unload the module. Remove the explictly
regulator_put() call and then we can also remove rk3399_dmcfreq_remove().

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>