PM / devfreq: tegra: remove unneeded variable

This variable is not used after initialization, so
remove it. And in order to unify the code style,
move the location where the dev_get_drvdata is called
by the way.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>