clk: at91: sam9x60-pll: use DIV_ROUND_CLOSEST_ULL

Use DIV_ROUND_CLOSEST_ULL() to avoid any inconsistency b/w the rate
computed in sam9x60_frac_pll_recalc_rate() and the one computed in
sam9x60_frac_pll_compute_mul_frac().

Fixes: 43b1bb4a ("clk: at91: clk-sam9x60-pll: re-factor to support plls with multiple outputs")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20211011112719.3951784-8-claudiu.beznea@microchip.com


Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>