sched/core: Fix warning introduced in __set_cpus_allowed_ptr

While porting commit f6df9e00 ("sched: add cpu isolation support"),
some of the changes from msm-4.9 weren't ported correctly and causing
below warning, fix the warning by porting missed changes from the commit.

[    3.242399] BUG: spinlock bad magic on CPU#0, kthreadd/2
[    3.327831] Call trace:
[    3.337494] dump_backtrace+0x0/0x378
[    3.353926] show_stack+0x20/0x2c
[    3.370526] __dump_stack+0x20/0x28
[    3.386463] dump_stack+0x70/0x94
[    3.402747] spin_bug+0xa4/0xb4
[    3.417610] do_raw_spin_lock+0xe8/0x118
[    3.435642] _raw_spin_lock_irqsave+0x34/0x44
[    3.454557] cpu_stop_queue_work+0x44/0x98
[    3.472231] stop_one_cpu+0x58/0xb0
[    3.488568] __set_cpus_allowed_ptr+0x1d0/0x20c
[    3.507621] set_cpus_allowed_ptr+0x28/0x34
[    3.526189] kthreadd+0x50/0x15c
[    3.541336] ret_from_fork+0x10/0x18

Change-Id: Icbe323323ba993c427eb2005ce74d96872477717
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>