i2o: hide unsafe ioctl on 64-bit

We get a warning about a broken pointer conversion on 64-bit architectures:

drivers/message/i2o/i2o_config.c: In function 'i2o_cfg_passthru':
drivers/message/i2o/i2o_config.c:893:19: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
         (p->virt, (void __user *)sg[i].addr_bus,
                   ^
drivers/message/i2o/i2o_config.c:953:10: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
         ((void __user *)sg[j].addr_bus, sg_list[j].virt,
          ^

This has clearly never worked right, so we can add an #ifdef around the code.
The driver was moved to staging in linux-4.0 and finally removed in 4.2,
so upstream does not have a fix for it.

The driver originally got this mostly right, though probably by accident.

Fixes: f4c2c15b ("[PATCH] Convert i2o to compat_ioctl")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>