clk: keystone: sci-clk: add 10% slack to set_rate

clk: keystone: sci-clk: add 10% slack to set_rate

Currently, we request exact clock rates from the firmware to be set with
set_rate. Due to some rounding errors and internal functionality of the
firmware itself, this can fail. Thus, add some slack to the set_rate
functionality so that we are always guaranteed to pass. The firmware
always attempts to use frequency as close to the target freq as
possible despite the slack given here.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Link: https://lore.kernel.org/r/20200907085740.1083-4-t-kristo@ti.com
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>