clk: renesas: r8a774c0: Fix LAST_DT_CORE_CLK

Enum LAST_DT_CORE_CLK needs updating as R8A774C0_CLK_CANFD
was recently added and it's the core clock with the highest
index.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Chris Paterson <chris.paterson2@renesas.com>
Fixes: 2a6efbc6 ("clk: renesas: r8a774c0: Add missing CANFD clock")
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>