powerpc/8xx: Erroneous double irq_eoi() on CPM IRQ in MPC8xx

irq_eoi() is already called by generic_handle_irq() so
it shall not be called a again

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <scottwood@freescale.com>