i40e: Fix calculating the number of queue pairs

If ADQ is enabled for a VF, then actual number of queue pair
is a number of currently available traffic classes for this VF.

Without this change the configuration of the Rx/Tx queues
fails with error.

Fixes: d29e0d23 ("i40e: missing input validation on VF message handling by the PF")
Signed-off-by: Grzegorz Szczurek <grzegorzx.szczurek@intel.com>
Signed-off-by: Jedrzej Jagielski <jedrzej.jagielski@intel.com>
Tested-by: Bharathi Sreenivas <bharathi.sreenivas@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>