Input: sx8654 - fix memory allocation check

We have been testing wrong variable when trying to make sure that input
allocation succeeded.

Reported by Coverity (CID 1295918).

Acked-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>