NFC: st95hf: Fix build error

NFC: st95hf: Fix build error

This fixes a build error on the mn10300 architecture:

drivers/nfc/st95hf/core.c:765:20: error: conflicting types for 'irq_handler'
   static irqreturn_t irq_handler(int irq, void  *st95hfcontext)
                       ^
   In file included from arch/mn10300/include/asm/reset-regs.h:16:0,
                    from arch/mn10300/include/asm/irq.h:18,
                    from include/linux/irq.h:26,
                    from arch/mn10300/include/asm/hardirq.h:16,
                    from include/linux/hardirq.h:8,
                    from include/linux/interrupt.h:12,
                    from drivers/nfc/st95hf/core.c:23:
   arch/mn10300/include/asm/exceptions.h:107:24: note: previous declaration of 'irq_handler' was here
    extern asmlinkage void irq_handler(void);

Signed-off-by: Shikha Singh <shikha.singh@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>