clk: fractional-divider: Move mask calculations out of lock

There is no need to calculate masks under the lock taken.
Move them out of it.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20240303121410.240761-1-andy.shevchenko@gmail.com


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