sched: Remove extra put_online_cpus() inside sched_setaffinity()

Commit:

sched: Remove get_online_cpus() usage

has left one extra put_online_cpus() inside sched_setaffinity(),
remove it to fix the WARN:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 3166 at kernel/cpu.c:84 put_online_cpus+0x43/0x70()
...
[<ffffffff810c3fef>] put_online_cpus+0x43/0x70 [
[<ffffffff810efd59>] sched_setaffinity+0x7d/0x1f9 [
...

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/526DD0EE.1090309@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>

idea is taken here -
https://github.com/franciscofranco/flo/commit/3bc17a9d03dad94983f085e2078eb4adc1901afd