i2c: uniphier_f: error out if bus speed is zero

There is code to divide by "bus_speed" some lines below.
To eliminate the possibility of division by zero, bail out if
"clock-frequency" is specified as zero.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-uniphier-f.c

@@ -466,6 +466,11 @@ static int uniphier_fi2c_clk_init(struct device *dev,
 	if (of_property_read_u32(np, "clock-frequency", &bus_speed))
 		bus_speed = UNIPHIER_FI2C_DEFAULT_SPEED;
 
+	if (!bus_speed) {
+		dev_err(dev, "clock-freqyency should not be zero\n");
+		return -EINVAL;
+	}
+
 	if (bus_speed > UNIPHIER_FI2C_MAX_SPEED)
 		bus_speed = UNIPHIER_FI2C_MAX_SPEED;