i40e: don't configure zero-size RSS table

In some rare cases, we might get a VSI with no queues. In this case, we
cannot configure RSS on this VSI as it will try to divide by zero when
configuring the lookup table.

Change-ID: I6ae173a7dd3481a081e079eb10eb80275de2adb0
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -8282,6 +8282,8 @@ static int i40e_pf_config_rss(struct i40e_pf *pf)
 	if (!vsi->rss_size)
 		vsi->rss_size = min_t(int, pf->alloc_rss_size,
 				      vsi->num_queue_pairs);
+	if (!vsi->rss_size)
+		return -EINVAL;
 
 	lut = kzalloc(vsi->rss_table_size, GFP_KERNEL);
 	if (!lut)