gpu: host1x: Fix memory leak of device names

In the Linux kernel, the following vulnerability has been resolved:

gpu: host1x: Fix memory leak of device names

The device names allocated by dev_set_name() need be freed

before module unloading, but they can not be freed because

the kobject's refcount which was set in device_initialize()

has not be decreased to 0.

As comment of device_add() says, if it fails, use only

put_device() drop the refcount, then the name will be

freed in kobejct_cleanup().

device_del() and put_device() can be replaced with

device_unregister(), so call it to unregister the added

successfully devices, and just call put_device() to the

not added device.

Add a release() function to device to avoid null release()

function WARNING in device_release(), it's empty, because

the context devices are freed together in

host1x_memory_context_list_free().