Input: tca8418_keypad - increase severity of failures in probe()

Failures to build a keymap, request an IRQ, or register input device are
fatal for the driver, therefore the messages should have "error" severity
instead of "debug".

Reviewed-by: Alban Bedel <alban.bedel@avionic-design.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>