mfd: 88pm886: Constify struct regmap_irq_chip and some other structures

'struct regmap_irq_chip' is not modified in this driver.

Constifying this structure moves some data to a read-only section, so
increase overall security, especially when the structure holds some
function pointers.

While at it, also constify some other structures.

On a x86_64, with allmodconfig, as an example:
Before:
======
   text	   data	    bss	    dec	    hex	filename
   5032	   3304	     64	   8400	   20d0	drivers/mfd/88pm886.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
   5800	   2536	     64	   8400	   20d0	drivers/mfd/88pm886.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/1681629840761e30494cb8920668710df60a81b8.1746996137.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Lee Jones <lee@kernel.org>

Author: tititiou36

drivers/mfd/88pm886.c

@@ -16,11 +16,11 @@ static const struct regmap_config pm886_regmap_config = {
 	.max_register = PM886_REG_RTC_SPARE6,
 };
 
-static struct regmap_irq pm886_regmap_irqs[] = {
+static const struct regmap_irq pm886_regmap_irqs[] = {
 	REGMAP_IRQ_REG(PM886_IRQ_ONKEY, 0, PM886_INT_ENA1_ONKEY),
 };
 
-static struct regmap_irq_chip pm886_regmap_irq_chip = {
+static const struct regmap_irq_chip pm886_regmap_irq_chip = {
 	.name = "88pm886",
 	.irqs = pm886_regmap_irqs,
 	.num_irqs = ARRAY_SIZE(pm886_regmap_irqs),
@@ -30,11 +30,11 @@ static struct regmap_irq_chip pm886_regmap_irq_chip = {
 	.unmask_base = PM886_REG_INT_ENA_1,
 };
 
-static struct resource pm886_onkey_resources[] = {
+static const struct resource pm886_onkey_resources[] = {
 	DEFINE_RES_IRQ_NAMED(PM886_IRQ_ONKEY, "88pm886-onkey"),
 };
 
-static struct mfd_cell pm886_devs[] = {
+static const struct mfd_cell pm886_devs[] = {
 	MFD_CELL_RES("88pm886-onkey", pm886_onkey_resources),
 	MFD_CELL_NAME("88pm886-regulator"),
 	MFD_CELL_NAME("88pm886-rtc"),