drm/xe/vf: Use single check when calling VF CCS functions

All xe_sriov_vf_ccs() functions but init() expect to be called
when initialization was successful and CCS handling is ready.

Update IS_VF_CCS_READY macro and use it as single entry guard.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Link: https://lore.kernel.org/r/20250908123025.747-5-michal.wajdeczko@intel.com