regulator: Factor out references to rdev in regulator_force_disable()

Don't go looking up the rdev pointer every time, just use a local variable
like everything else.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>

diff --cc drivers/regulator/core.c
Simple merge