genirq: NULL struct irq_desc's member 'name' in dynamic_irq_cleanup()

If the member 'name' of the irq_desc structure happens to point to a
character string that is resident within a kernel module, problems ensue
if that module is rmmod'd (at which time dynamic_irq_cleanup() is called)
and then later show_interrupts() is called by someone.

It is also not a good thing if the character string resided in kmalloc'd
space that has been kfree'd (after having called dynamic_irq_cleanup()).
dynamic_irq_cleanup() fails to NULL the 'name' member and
show_interrupts() references it on a few architectures (like h8300, sh and
x86).

Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>