PM / devfreq: rk3399_dmc: Fix duplicated opp table on reload.

The opp table is not removed when the driver is unloaded neither when
there is an error within probe, so if the driver is reloaded the opp
core shows the following warning:

  rk3399-dmc-freq dmc: _opp_add: duplicate OPPs detected. Existing: freq:
               200000000, volt: 900000, enabled: 1. New: freq: 200000000,
               volt: 900000, enabled: 1
  rk3399-dmc-freq dmc: _opp_add: duplicate OPPs detected. Existing: freq:
               400000000, volt: 900000, enabled: 1. New: freq: 400000000,
               volt: 900000, enabled: 1
  rk3399-dmc-freq dmc: _opp_add: duplicate OPPs detected. Existing: freq:
               666000000, volt: 900000, enabled: 1. New: freq: 666000000,
               volt: 900000, enabled: 1
  rk3399-dmc-freq dmc: _opp_add: duplicate OPPs detected. Existing: freq:
               800000000, volt: 900000, enabled: 1. New: freq: 800000000,
               volt: 900000, enabled: 1
  rk3399-dmc-freq dmc: _opp_add: duplicate OPPs detected. Existing: freq:
               928000000, volt: 900000, enabled: 1. New: freq: 928000000,
               volt: 900000, enabled: 1

This patch fixes the error path in the probe function and adds a .remove
function to properly cleanup the opp table on unloading.

Fixes: 5a893e31 (PM / devfreq: rockchip: add devfreq driver for rk3399 dmc)
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>