i40e: Fix the Tx ring qset handle when DCB reconfigures

When DCB is reconfigured to single TC the driver did not reset the
Tx ring Qset handle to the correct mapping; which caused Tx queue
disable timeouts.

Change-ID: I4da5915ec92a83c281b478d653fae6ef1b72edfe
Signed-off-by: Neerav Parikh <neerav.parikh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>