hwmon: (pwm-fan) Report probe errors consistently

Printing the error code for a failure provides a head-start for
debugging, since it's often sufficient to pinpoint the origin of the
failure. We already do this for some probe-failure messages, so let's
make the rest of them consistent.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>