powerpc/mpic: constify copied structure

The mpic_ipi_chip and mpic_irq_ht_chip structures are only copied
into other structures, so make them const.

The opportunity for this change was found using Coccinelle.
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1577864614-5543-10-git-send-email-Julia.Lawall@inria.fr

arch/powerpc/sysdev/mpic.c

@@ -964,7 +964,7 @@ static struct irq_chip mpic_irq_chip = {
 };
 
 #ifdef CONFIG_SMP
-static struct irq_chip mpic_ipi_chip = {
+static const struct irq_chip mpic_ipi_chip = {
 	.irq_mask	= mpic_mask_ipi,
 	.irq_unmask	= mpic_unmask_ipi,
 	.irq_eoi	= mpic_end_ipi,
@@ -978,7 +978,7 @@ static struct irq_chip mpic_tm_chip = {
 };
 
 #ifdef CONFIG_MPIC_U3_HT_IRQS
-static struct irq_chip mpic_irq_ht_chip = {
+static const struct irq_chip mpic_irq_ht_chip = {
 	.irq_startup	= mpic_startup_ht_irq,
 	.irq_shutdown	= mpic_shutdown_ht_irq,
 	.irq_mask	= mpic_mask_irq,