ice: Change CGU regs struct to anonymous

ice: Change CGU regs struct to anonymous

Simplify the code by using anonymous struct in CGU registers instead of
naming each structure 'field'.

Suggested-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Signed-off-by: Karol Kolacinski <karol.kolacinski@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20240528-next-2024-05-28-ptp-refactors-v1-8-c082739bb6f6@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>