panvk: Fix assert

Fix defect reported by Coverity Scan.

Assign instead of compare (PW.ASSIGN_WHERE_COMPARE_MEANT)
assign_where_compare_meant: use of "=" where "==" may have been intended

Fixes: 0e74b6eda9 ("panvk: Add support for layered rendering")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30181>

src/panfrost/vulkan/panvk_vX_shader.c

@@ -119,7 +119,7 @@ panvk_lower_sysvals(nir_builder *b, nir_instr *instr, void *data)
       break;
 
    case nir_intrinsic_load_layer_id:
-      assert(b->shader->info.stage = MESA_SHADER_FRAGMENT);
+      assert(b->shader->info.stage == MESA_SHADER_FRAGMENT);
       val = load_sysval_from_push_const(b, SYSVAL(graphics, layer_id), bit_size,
                                         num_comps);
       break;