Impact: clean up sparseirq fallout on random.c

Ingo suggested to change some ifdef from SPARSE_IRQ to GENERIC_HARDIRQS
so we could some #ifdef later if all arch support genirq
Signed-off-by: NYinghai Lu <yinghai@kernel.org>
Acked-by: NMatt Mackall <mpm@selenic.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>