sched: fix reference to wrong cfs_rq

Commit 7db16c8c (sched: Fix SCHED_HRTICK bug leading to late preemption
of tasks) introduced a bug in sched_slice() calculation by using wrong
cfs_rq for tasks. rq->cfs was incorrectly used as task's cfs_rq, rather
than the correct one to which they belonged.

Fix the bug by using correct cfs_rq for tasks.

Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
msm: kgsl: Don't access context memory after it's freed

Context memory was potentially accessed after being freed. Fix this
by incrementing the context's refcount at strategic places.

Change-Id: I31049bdd3eb9ac52160ca593619fcc8a32d4ddee
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>