auxdisplay: ht16k33: Remove unneeded error check in keypad probe()

There is no need to check the return code of input_register_device(),
just propagate it to the caller.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Robin van der Gracht <robin@protonic.nl>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>