sched: initialize env->flags variable to 0

env->flags and env->new_dst_cpu fields are not initialized in
load_balance() function. As a result, load_balance() could wrongly see
LBF_SOME_PINNED flag set and access (bogus) new_dst_cpu's runqueue
leading to invalid memory reference. Fix this by initializing
env->flags field to 0. While we are at it, fix similar issue in
active_load_balance_cpu_stop() function, although there is no harm
present currently in that function with uninitialized env->flags
variable.

Change-Id: Ied470b0abd65bf2ecfa33fa991ba554a5393f649
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>