clk: tegra: divider: Check UART's divider enable-bit state on rate's recalculation

UART clock is divided using divisor values from DLM/DLL registers when
enable-bit is unset in clk register and clk's divider configuration isn't
taken onto account in this case. This doesn't cause any problems, but
let's add a check for the divider's enable-bit state, for consistency.

Acked-by: Peter De Schrijver <[e-mail]>
Signed-off-by: Dmitry Osipenko <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

drivers/clk/tegra/clk-divider.c

···
 	int div, mul;
 	u64 rate = parent_rate;
 
-	reg = readl_relaxed(divider->reg) >> divider->shift;
-	div = reg & div_mask(divider);
+	reg = readl_relaxed(divider->reg);
+
+	if ((divider->flags & TEGRA_DIVIDER_UART) &&
+	    !(reg & PERIPH_CLK_UART_DIV_ENB))
+		return rate;
+
+	div = (reg >> divider->shift) & div_mask(divider);
 
 	mul = get_mul(divider);
 	div += mul;