net: include io.h in sja1000_of_platform.c for iounmap etc

fixes these build errors:

drivers/net/can/sja1000/sja1000_of_platform.c: In function 'sja1000_ofp_read_reg':
drivers/net/can/sja1000/sja1000_of_platform.c:61:2: error: implicit declaration of function 'in_8'
drivers/net/can/sja1000/sja1000_of_platform.c: In function 'sja1000_ofp_write_reg':
drivers/net/can/sja1000/sja1000_of_platform.c:67:2: error: implicit declaration of function 'out_8'
drivers/net/can/sja1000/sja1000_of_platform.c: In function 'sja1000_ofp_remove':
drivers/net/can/sja1000/sja1000_of_platform.c:81:2: error: implicit declaration of function 'iounmap'
drivers/net/can/sja1000/sja1000_of_platform.c: In function 'sja1000_ofp_probe':
drivers/net/can/sja1000/sja1000_of_platform.c:113:2: error: implicit declaration of function 'ioremap_nocache'
drivers/net/can/sja1000/sja1000_of_platform.c:113:7: warning: assignment makes pointer from integer without a cast

Caused by commit b7f080cfe223 ("net: remove mm.h inclusion from
netdevice.h").

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>