clk: vc5: Use `clamp()` to restrict PLL range

The VCO frequency needs to be within a certain range and the driver
enforces this.

Make use of the clamp macro to implement this instead of open-coding it.
This makes the code a bit shorter and also semanticly stronger.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20230114233500.3294789-1-lars@metafoo.de


Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>