power: supply: ltc2941: clean up error messages

Replace dev_err() with dev_err_probe() in probe() and extend register
access failure messages. dev_err()s in _reset() are removed as they
are redundant: register access wrappers already log the error.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>