Input: xpad - remove usage of the deprecated ida_simple_xx() API

ida_alloc() and ida_free() should be preferred to the deprecated
ida_simple_get() and ida_simple_remove().

This is less verbose.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/a3e30e30f18cc5d6f032c8013ce9d900c8e223e5.1702228806.git.christophe.jaillet@wanadoo.fr


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