clk: Compute masks for fractional_divider clk when needed.

There is no real need to pre-compute mmask and nmask when handling
fractional_divider clk.

They can be computed when needed.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/0fd6357242c974259c9e034c6e28a0391c480bf0.1680423909.git.christophe.jaillet@wanadoo.fr


Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>