i2c: jz4780: Fix build for m68k and sparc64

Fix:

drivers/i2c/busses/i2c-jz4780.c: In function 'jz4780_i2c_readw':
drivers/i2c/busses/i2c-jz4780.c:181:2: error:
		implicit declaration of function 'readw'
drivers/i2c/busses/i2c-jz4780.c: In function 'jz4780_i2c_writew':
drivers/i2c/busses/i2c-jz4780.c:187:2: error:
		implicit declaration of function 'writew'

seen with sparc64:allmodconfig and m68k:allmodconfig.

The driver has to include linux/io.h.

Fixes: ba92222e ("i2c: jz4780: Add i2c bus controller driver
	for Ingenic JZ4780")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>