clk: at91: Constify irq_domain_ops

The irq_domain_ops are not modified by the driver and the irqdomain core
code accepts pointer to a const data.
Signed-off-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

drivers/clk/at91/pmc.c

@@ -153,7 +153,7 @@ static int pmc_irq_domain_xlate(struct irq_domain *d,
 	return 0;
 }
 
-static struct irq_domain_ops pmc_irq_ops = {
+static const struct irq_domain_ops pmc_irq_ops = {
 	.map	= pmc_irq_map,
 	.xlate	= pmc_irq_domain_xlate,
 };