MIPS: Add common plat_irq_dispatch declaration

Add common declaration to get rid of following sparse warning: "symbol
'plat_irq_dispatch' was not declared. Should it be static?"
Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Cc: Linux MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/7539/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/cavium-octeon/setup.c

@@ -263,7 +263,6 @@ static uint64_t crashk_size, crashk_base;
 static int octeon_uart;
 
 extern asmlinkage void handle_int(void);
-extern asmlinkage void plat_irq_dispatch(void);
 
 /**
  * Return non zero if we are currently running in the Octeon simulator

arch/mips/include/asm/irq.h

@@ -26,6 +26,8 @@ static inline int irq_canonicalize(int irq)
 #define irq_canonicalize(irq) (irq)	/* Sane hardware, sane code ... */
 #endif
 
+asmlinkage void plat_irq_dispatch(void);
+
 extern void do_IRQ(unsigned int irq);
 
 extern void arch_init_irq(void);