clk: fixed-factor: round_rate should use do_div

clk->rate = parent->rate / div * mult

The formula is OK. But it may overflow while we do operate with
unsigned long. So use do_div instead.
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
[mturquette@linaro.org: improved $SUBJECT]

drivers/clk/clk-fixed-factor.c

@@ -28,8 +28,11 @@ static unsigned long clk_factor_recalc_rate(struct clk_hw *hw,
 		unsigned long parent_rate)
 {
 	struct clk_fixed_factor *fix = to_clk_fixed_factor(hw);
+	unsigned long long int rate;
 
-	return parent_rate * fix->mult / fix->div;
+	rate = (unsigned long long int)parent_rate * fix->mult;
+	do_div(rate, fix->div);
+	return (unsigned long)rate;
 }
 
 static long clk_factor_round_rate(struct clk_hw *hw, unsigned long rate,