generic-ipi: Fix misleading smp_call_function*() description

After commit:8969a5ed


"generic-ipi: remove kmalloc()", wait = 0 can be guaranteed.

Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Nick Piggin <npiggin@suse.de>
LKML-Reference: <1256210374-25354-1-git-send-email-sheng@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>