m68k: Add missing ioport_unmap()

drivers/net/ethernet/cirrus/cs89x0.c: In function ‘cs89x0_ioport_probe’:
drivers/net/ethernet/cirrus/cs89x0.c:1629: error: implicit declaration of function ‘ioport_unmap’

Add the missing ioport_unmap() implementation, and convert ioport_map()
from a macro to a static inline function while we're at it (both copied
from asm-generic).
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/include/asm/io_mm.h

@@ -510,6 +510,13 @@ static inline void memcpy_toio(volatile void __iomem *dst, const void *src, int
  */
 #define xlate_dev_kmem_ptr(p)	p
 
-#define ioport_map(port, nr)	((void __iomem *)(port))
+static inline void __iomem *ioport_map(unsigned long port, unsigned int nr)
+{
+	return (void __iomem *) port;
+}
+
+static inline void ioport_unmap(void __iomem *p)
+{
+}
 
 #endif /* _IO_H */