Calling rte_eth_dev_get_dcb_info to get dcb info from i40e
driver if VMDQ is disabled, results in a segmentation fault.
This patch fixes it by treating VMDQ and No-VMDQ respectively
when querying dcb information.
Fixes: 5135f3ca49a7 ("i40e: enable DCB in VMDQ VSIs")
Signed-off-by: Jingjing Wu <jingjing.wu@intel.com>