Input: input_event - fix the CONFIG_SPARC64 mixup

Arnd Bergmann pointed out that CONFIG_* cannot be used in a uapi header.
Override with an equivalent conditional.

Fixes: 2e746942 ("Input: input_event - provide override for sparc64")
Fixes: 152194fe

 ("Input: extend usable life of event timestamps to 2106 on 32 bit systems")
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>