st/mesa: fix pbo download store image type

There's generally not too big of a difference between 1D (default) and
buffer, but can't hurt to be accurate.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12319>

src/mesa/state_tracker/st_pbo.c

@@ -569,7 +569,8 @@ create_fs(struct st_context *st, bool download,
                             nir_vec4(&b, pbo_addr, zero, zero, zero),
                             zero,
                             result,
-                            nir_imm_int(&b, 0));
+                            nir_imm_int(&b, 0),
+                            .image_dim = GLSL_SAMPLER_DIM_BUF);
    } else {
       nir_variable *color =
          nir_variable_create(b.shader, nir_var_shader_out, glsl_vec4_type(),