clk: at91: generated: Truncate divisor to GENERATED_MAX_DIV + 1

In clk_generated_determine_rate(), if the divisor is greater than
GENERATED_MAX_DIV + 1, then the wrong best_rate will be returned.
If clk_generated_set_rate() will be called later with this wrong
rate, it will return -EINVAL, so the generated clock won't change
its value. Do no let the divisor be greater than GENERATED_MAX_DIV + 1.

Fixes: 8c7aa632 ("clk: at91: clk-generated: remove useless divisor loop")
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>