IB/mlx5: Increase flow table reference count in create rule

Move the reference count increasing of flow table to be in
create_flow_rule, it will increase the reference count for each rule
creation and not for each flow.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>