clk: stm32f: fix setting of LCD clock

clk: stm32f: fix setting of LCD clock

Set pllsaidivr only if the PLLSAIR output frequency is an exact multiple
of the pixel clock rate. Otherwise, we search through all combinations
of pllsaidivr * pllsair and use the one which gives the rate closest to
requested one.

Fixes: 5e993508cb25 ("clk: clk_stm32f: Add set_rate for LTDC clock")
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>