Input: twl4030-pwrbutton - use dev_err for errors

Use dev_err() to output errors instead of dev_dbg().

Signed-off-by: Sebastian Reichel <sre@debian.org>
Reviewed-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>