hwmon: (lm90) Unregister hwmon device if interrupt setup fails

Commit 109b1283 (hwmon: (lm90) Add support to handle IRQ) introduced
interrupt support. Its error handling code fails to unregister the already
registered hwmon device.

Fixes: 109b1283
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>