m68k: atari: Make Atari ROM port I/O write macros return void

The macros implementing Atari ROM port I/O writes do not cast away their
output, unlike similar implementations for other I/O buses.
When they are combined using conditional expressions in the definitions of
outb() and friends, this triggers sparse warnings like:

    drivers/net/appletalk/cops.c:382:17: error: incompatible types in conditional expression (different base types):
    drivers/net/appletalk/cops.c:382:17:    unsigned char
    drivers/net/appletalk/cops.c:382:17:    void

Fix this by adding casts to "void".

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Michael Schmitz <schmitzmic@gmail.com>
Link: https://lore.kernel.org/r/c15bedc83d90a14fffcd5b1b6bfb32b8a80282c5.1653057096.git.geert@linux-m68k.org