RDMA/core: Fix double put of resource

Do not decrease the reference count of resource tracker object twice in
the error flow of res_get_common_doit.

Fixes: c5dfe0ea ("RDMA/nldev: Add resource tracker doit callback")
Link: https://lore.kernel.org/r/20200507062942.98305-1-leon@kernel.org


Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>