drm/amdkfd: use mmu_notifier_put

The sequence of mmu_notifier_unregister_no_release(),
mmu_notifier_call_srcu() is identical to mmu_notifier_put() with the
free_notifier callback.

As this is the last user of those APIs, converting it means we can drop
them.

Link: https://lore.kernel.org/r/20190806231548.25242-11-jgg@ziepe.ca


Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>