MIPS: jz4740: fix build error in irq.h

kernelci found build error on the 3.18 stable tree that don't
show up in later versions:

arch/mips/jz4740/irq.h:21:38: error: 'struct irq_data' declared inside parameter list will not be visible outside of this definition or declaration [-Werror]
arch/mips/jz4740/irq.h:20:39: error: 'struct irq_data' declared inside parameter list will not be visible outside of this definition or declaration [-Werror]
include/linux/irqdesc.h:92:33: error: 'NR_IRQS' undeclared here (not in a function)
arch/mips/jz4740/irq.c:91:41: error: 'JZ4740_IRQ_BASE' undeclared (first use in this function)
arch/mips/jz4740/irq.c:68:6: error: conflicting types for 'jz4740_irq_resume'
arch/mips/jz4740/irq.c:62:6: error: conflicting types for 'jz4740_irq_suspend'
arch/mips/jz4740/irq.c:49:39: error: 'JZ4740_IRQ_BASE' undeclared (first use in this function)
arch/mips/jz4740/gpio.c:47:32: error: initializer element is not constant
arch/mips/jz4740/gpio.c:46:32: error: initializer element is not constant
arch/mips/jz4740/gpio.c:45:32: error: initializer element is not constant
arch/mips/jz4740/gpio.c:44:32: error: initializer element is not constant
arch/mips/jz4740/gpio.c:447:22: error: assignment from incompatible pointer type [-Werror=incompatible-pointer-types]
arch/mips/jz4740/gpio.c:446:23: error: assignment from incompatible pointer type [-Werror=incompatible-pointer-types]
arch/mips/jz4740/gpio.c:427:14: error: implicit declaration of function 'JZ4740_IRQ_INTC_GPIO' [-Werror=implicit-function-declaration]
arch/mips/jz4740/gpio.c:269:9: error: implicit declaration of function 'JZ4740_IRQ_GPIO' [-Werror=implicit-function-declaration]

The problem seems to be caused by commit 83bc7692 ("MIPS: JZ4740: Use
generic irq chip") from linux-3.2, but only showed up in a defconfig
build when qi_lb60_defconfig was added in linux-3.13 and that configuration
never successfully built.

The code has changed in a number of ways before 4.4, which builds fine.
While I did not bisect the problem to a specific change, I found a simple
fix by including the obviously missing header.

Cc: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/mips/jz4740/irq.h

@@ -16,7 +16,9 @@
 #define __MIPS_JZ4740_IRQ_H__
 
 #include <linux/irq.h>
+#include <asm/mach-jz4740/irq.h>
 
+struct irq_data;
 extern void jz4740_irq_suspend(struct irq_data *data);
 extern void jz4740_irq_resume(struct irq_data *data);