Now that input core supports devres-managed input devices we can clean
up this driver a bit.

Link: https://lore.kernel.org/r/X/qfJKiM21uyksYl@google.comTested-by: NTony Lindgren <tony@atomide.com>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>