sh: clkfwk: bugfix: use clk_reparent() for div6 clocks

Various problems will happen if clk parent was set up directly.
it should use clk_reparent()

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>