hwmon: (lm80) Fix missing unlock on error in set_fan_div()

[ Upstream commit 07bd14ccc3049f9c0147a91a4227a571f981601a ]

Add the missing unlock before return from function set_fan_div()
in the error handling case.

Fixes: c9c63915519b ("hwmon: (lm80) fix a missing check of the status of SMBus read")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>