irqchip/ingenic-tcu: Use correctly sized arguments for bit field

The find.h APIs are designed to be used only on unsigned long arguments.
This can technically result in a over-read, but it is harmless in this
case. Regardless, fix it to avoid the warning seen under -Warray-bounds,
which we'd like to enable globally:

In file included from ./include/linux/bitmap.h:9,
                 from ./include/linux/cpumask.h:12,
                 from ./include/linux/smp.h:13,
                 from ./include/linux/lockdep.h:14,
                 from ./include/linux/mutex.h:17,
                 from ./include/linux/notifier.h:14,
                 from ./include/linux/clk.h:14,
                 from drivers/irqchip/irq-ingenic-tcu.c:7:
drivers/irqchip/irq-ingenic-tcu.c: In function 'ingenic_tcu_intc_cascade':
./include/linux/find.h:40:23: warning: array subscript 'long unsigned int[0]' is partly outside array bounds of 'uint32_t[1]' {aka 'unsigned int[1]'} [-Warray-bounds]
   40 |                 val = *addr & GENMASK(size - 1, offset);
      |                       ^~~~~
drivers/irqchip/irq-ingenic-tcu.c:30:18: note: while referencing 'irq_reg'
   30 |         uint32_t irq_reg, irq_mask;
      |                  ^~~~~~~
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211215232457.2069969-1-keescook@chromium.org

drivers/irqchip/irq-ingenic-tcu.c

@@ -28,6 +28,7 @@ static void ingenic_tcu_intc_cascade(struct irq_desc *desc)
 	struct irq_chip_generic *gc = irq_get_domain_generic_chip(domain, 0);
 	struct regmap *map = gc->private;
 	uint32_t irq_reg, irq_mask;
+	unsigned long bits;
 	unsigned int i;
 
 	regmap_read(map, TCU_REG_TFR, &irq_reg);
@@ -36,8 +37,9 @@ static void ingenic_tcu_intc_cascade(struct irq_desc *desc)
 	chained_irq_enter(irq_chip, desc);
 
 	irq_reg &= ~irq_mask;
+	bits = irq_reg;
 
-	for_each_set_bit(i, (unsigned long *)&irq_reg, 32)
+	for_each_set_bit(i, &bits, 32)
 		generic_handle_domain_irq(domain, i);
 
 	chained_irq_exit(irq_chip, desc);