powerpc/mpc8610_hpcd: Do not use "/" in interrupt names

It may trigger a warning in fs/proc/generic.c:__xlate_proc_name() when
trying to add an entry for the interrupt handler to sysfs.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>