clk: starfive: Simplify .determine_rate()

jh71x0_clk_mux_determine_rate() is the same as __clk_mux_determine_rate(),
so use the latter to save some LoC.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/085541814ebe2543cb7e8a31004c0da3e7d5b6eb.1688760111.git.christophe.jaillet@wanadoo.fr


Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>