net/mlx5: fs, assert null dest pointer when dest_num is 0

net/mlx5: fs, assert null dest pointer when dest_num is 0

Currently create_flow_handle() assumes a null dest pointer when there
are no destinations.
This might not be the case as the caller may pass an allocated dest
array while setting the dest_num parameter to 0.

Assert null dest array for flow rules that have no destinations (e.g. drop
rule).

Signed-off-by: Oz Shlomo <ozsh@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Link: https://lore.kernel.org/r/20221203221337.29267-3-saeed@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>