Currently, c_idle is declared in the stack, and thus, have no static address.

Peter Zijlstra points out this simple solution, in which c_idle.work
is initializated separatedly. Note that the INIT_WORK macro has a static
declaration of a key inside.
Signed-off-by: NGlauber Costa <gcosta@redhat.com>
Acked-by: NPeter Zijlstra <pzijlstr@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>