intel/isl: Explicitly set offset_B = 0 in get_uncomp_surf for arrays

The only user of this case is iris which initializes offset_B to 0 so
there's no real bug here.  However, it is unexpected from an API PoV.

Fixes: 9946120d2b "intel/isl: Add more cases to isl_surf_get_uncompressed_surf"
Acked-by: Ivan Briano <ivan.briano@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11765>

src/intel/isl/isl.c

@@ -2892,6 +2892,9 @@ isl_surf_get_uncompressed_surf(const struct isl_device *dev,
       *ucompr_surf = *surf;
       ucompr_surf->levels = 1;
 
+      /* The surface mostly stays as-is; there is no offset */
+      *offset_B = 0;
+
       /* The view remains the same */
       *ucompr_view = *view;
    } else {