ANDROID: Fixup!: sched/fair.c: Set SchedTune specific struct energy_env.task

This has to be done in the caller function of energy_diff() version of
SchedTune to avoid Null pointer dereference in energy_diff().

Change-Id: I3f0f68dbd11efb15bbb3b1832f8294419ed85241
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
(cherry picked from commit 14531d4e245d063f713ee5ed835df958e6c7838f)
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Quentin Perret <quentin.perret@arm.com>