MIPS: vpe-mt: fix possible memory leak while module exiting

Afer commit 1fa5ae85 ("driver core: get rid of struct device's
bus_id string array"), the name of device is allocated dynamically,
it need be freed when module exiting, call put_device() to give up
reference, so that it can be freed in kobject_cleanup() when the
refcount hit to 0. The vpe_device is static, so remove kfree() from
vpe_device_release().

Fixes: 1fa5ae85 ("driver core: get rid of struct device's bus_id string array")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>