drm/xe/stolen: rename fb to node in stolen compat header
It's more about node than fb, and this makes more sense now that the
struct is also named intel_stolen_node.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/71a7872e47da5f3fbe61cc21723bfcf8ff6518b8.1758732183.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>