drm/xe: Allow const pointer when checking SR-IOV mode

It seems that more and more parts of the driver code rely on
having only a const pointer to the xe_device. Allow to check
SR-IOV mode in that code as well.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240617122613.553-1-michal.wajdeczko@intel.com