mfd: madera: Remove unused forward reference

The madera_irqchip_pdata struct was replaced by the irq_flags
member of struct madera_pdata so the forward reference is
obsolete.
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

include/linux/mfd/madera/pdata.h

@@ -24,7 +24,6 @@
 
 struct gpio_desc;
 struct pinctrl_map;
-struct madera_irqchip_pdata;
 struct madera_codec_pdata;
 
 /**