ice: Fix corner case when switching from IEEE to CEE

While testing DCB for a corner case in which mode is switched from IEEE to
CEE and pfc_ena bitmask unchanged then DCBX mode doesn't get updated.

This is happening because the function ice_dcb_get_mode() is called
in a "no change detected block" instead of "change detected block".

Signed-off-by: Avinash JD <avinash.dayanand@intel.com>
Signed-off-by: Scott Register <scottx.register@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>