clk: at91: clk-master: check if div or pres is zero

Check if div or pres is zero before using it as argument for ffs().
In case div is zero ffs() will return 0 and thus substracting from
zero will lead to invalid values to be setup in registers.

Fixes: 7a110b9 ("clk: at91: clk-master: re-factor master clock")
Fixes: 75c8814 ("clk: at91: clk-master: add master clock support for SAMA7G5")
Signed-off-by: Claudiu Beznea <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Acked-by: Nicolas Ferre <[email protected]>
Signed-off-by: Stephen Boyd <[email protected]>

Author: claudiubeznea

drivers/clk/at91/clk-master.c

@@ -344,7 +344,7 @@ static int clk_master_pres_set_rate(struct clk_hw *hw, unsigned long rate,
 
 	else if (pres == 3)
 		pres = MASTER_PRES_MAX;
-	else
+	else if (pres)
 		pres = ffs(pres) - 1;
 
 	spin_lock_irqsave(master->lock, flags);
@@ -757,7 +757,7 @@ static int clk_sama7g5_master_set_rate(struct clk_hw *hw, unsigned long rate,
 
 	if (div == 3)
 		div = MASTER_PRES_MAX;
-	else
+	else if (div)
 		div = ffs(div) - 1;
 
 	spin_lock_irqsave(master->lock, flags);