radeon: fix missing stencil_tile_mode initialisation in the linear/fallback case
../radeon/radeon_surface.c:1611:13: error: 'stencil_tile_mode' may be used uninitialized [-Werror=maybe-uninitialized]
1611 | r = si_surface_init_1d(surf_man, surf, surf->stencil_level, 1, stencil_tile_mode, surf->bo_size, 0);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~