clk: sci-clk: add slack to clk-set-rate passed to firmware

Add slack to the clock frequency parameters passed to firmware within
clk_set_rate. min-freq is changed to 0 and max-rate is changed to
ULONG_MAX. This fixes certain issues with pll clock rounding when the
firmware is not able to set the frequency exactly to the target, the
current implementation fails if the available frequency is even 1Hz off
the target. With the change, the firmware still tries its best to set
the frequency as close as possible to the target.

Reported-by: Vishal Mahaveer <vishalm@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>