hwmon: (it87) Test for error in it87_update_device

Handle errors from it87_update_device(), which currently only occurs if
SMBus access locking fails.

Signed-off-by: Frank Crawford <frank@crawford.emu.id.au>
[groeck: Fixed handling in show_temp_type()]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>