Input: wacom_i2c - switch to using managed resources

This simplifies error unwinding path and allows us to get rid of
remove() method.

Reviewed-by: Alistair Francis <alistair@alistair23.me>
Link: https://lore.kernel.org/r/20210321220043.318239-2-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>