clk: uniphier: Fix update register for CPU-gear

Need to set the update bit in UNIPHIER_CLK_CPUGEAR_UPD to update
the CPU-gear value.

Fixes: d08f1f0d ("clk: uniphier: add CPU-gear change (cpufreq) support")
Cc: linux-stable@vger.kernel.org
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>