video: ssd1307fb: add the missed regulator_disable

The driver forgets to disable the regulator in remove like what is done
in probe failure.
Add the missed call to fix it.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Tested-by: Michal Vokáč <michal.vokac@ysoft.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191118114150.25724-1-hslester96@gmail.com