Input: gameport - use IS_REACHABLE() instead of open-coding it

Replace an open-coded preprocessor conditional with an equivalent helper.

Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/ZKYLLmsdCH0Gp7TO@google.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>