tgsi: use enum for interpolate-mode

Reviewed-by: Yonggang Luo <luoyonggang@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24002>

src/gallium/auxiliary/tgsi/tgsi_two_side.c

@@ -54,7 +54,7 @@ struct two_side_transform_context
    uint num_inputs;
    uint face_input;           /**< index of the FACE input */
    uint front_color_input[2]; /**< INPUT regs */
-   uint front_color_interp[2];/**< TGSI_INTERPOLATE_x */
+   enum tgsi_interpolate_mode front_color_interp[2];/**< TGSI_INTERPOLATE_x */
    uint back_color_input[2];  /**< INPUT regs */
    uint new_colors[2];        /**< TEMP regs */
 };