m68k: amiga: Add linux/irq.h to make it compile again

The removal of linux/irq.h from kernel_stat.h causes 

 arch/m68k/amiga/cia.c:171: error: 'handle_simple_irq' undeclared

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/m68k/amiga/cia.c

@@ -18,6 +18,7 @@
 #include <linux/init.h>
 #include <linux/seq_file.h>
 #include <linux/interrupt.h>
+#include <linux/irq.h>
 
 #include <asm/irq.h>
 #include <asm/amigahw.h>