vme: fake: remove unexpected unlock in fake_master_set()

image->lock is unlocked in some error handling path without take the
lock, so remove those unexpected unlock.

Fixes: 658bcdae ("vme: Adding Fake VME driver")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>