sched/numa: Reflow task_numa_group() to avoid a compiler warning

Reflow the function a bit because GCC gets confused:

  kernel/sched/fair.c: In function ‘task_numa_fault’:
  kernel/sched/fair.c:1448:3: warning: ‘my_grp’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  kernel/sched/fair.c:1463:27: note: ‘my_grp’ was declared here

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-6ebt6x7u64pbbonq1khqu2z9@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>