pinctrl: rockchip: make rockchip_irq_gc_mask_set_bit static

The rockchip_irq_gc_mask_set_bit() function is not exported our used
outside of ppinctrl-rockchip.c so fix the following sparse error by
making it static:

drivers/pinctrl/pinctrl-rockchip.c:2010:6: warning:
  symbol 'rockchip_irq_gc_mask_set_bit' was not declared.
  Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinctrl-rockchip.c

@@ -2007,7 +2007,7 @@ static void rockchip_irq_gc_mask_clr_bit(struct irq_data *d)
 	irq_gc_mask_clr_bit(d);
 }
 
-void rockchip_irq_gc_mask_set_bit(struct irq_data *d)
+static void rockchip_irq_gc_mask_set_bit(struct irq_data *d)
 {
 	struct irq_chip_generic *gc = irq_data_get_irq_chip_data(d);
 	struct rockchip_pin_bank *bank = gc->private;