RDMA/core: Update write interface to use automatic object lifetime

The automatic object lifetime model allows us to change the write()
interface to have the same logic as the ioctl() path. Update the
create/alloc functions to be in the following format, so the code flow
will be the same:

 * Allocate objects
 * Initialize them
 * Call to the drivers, this is last step that is allowed to fail
 * Finalize object
 * Return response and allow to core code to handle abort/commit
   respectively.

Link: https://lore.kernel.org/r/20200719052223.75245-3-leon@kernel.orgSigned-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>