RDMA/cma: Rename cma_device ref/deref helpers to to get/put

Helper functions which increment/decrement reference count of the
structure read better when they are named with the get/put suffix.

Hence, rename cma_ref/deref_dev() to cma_dev_get/put().

Link: https://lore.kernel.org/r/20200126142652.104803-5-leon@kernel.org
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>