clk: ingenic/TCU: Fix round_rate returning error

When requesting a rate superior to the parent's rate, it would return
-EINVAL instead of simply returning the parent's rate like it should.

Fixes: 4f89e4b8

 ("clk: ingenic: Add driver for the TCU clocks")
Cc: stable@vger.kernel.org
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lkml.kernel.org/r/20200213161952.37460-2-paul@crapouillou.net
Signed-off-by: Stephen Boyd <sboyd@kernel.org>