net/mlx5e: reset XPS on error flow if netdev isn't registered yet

mlx5e_attach_netdev can be called prior to registering the netdevice:
Example stack:

ipoib_new_child_link ->
ipoib_intf_init->
rdma_init_netdev->
mlx5_rdma_setup_rn->

mlx5e_attach_netdev->
mlx5e_num_channels_changed ->
mlx5e_set_default_xps_cpumasks ->
netif_set_xps_queue ->
__netif_set_xps_queue -> kmalloc

If any later stage fails at any point after mlx5e_num_channels_changed()
returns, XPS allocated maps will never be freed as they
are only freed during netdev unregistration, which will never happen for
yet to be registered netdevs.

Fixes: 3909a12e ("net/mlx5e: Fix configuration of XPS cpumasks and netdev queues in corner cases")
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>