mmc: core: Fix warning and undefined behavior in mmc voltage handling

!voltage_ranges is tested for too late, allowing warning and undefined
behavior. Fix that.
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/host.c

@@ -363,11 +363,11 @@ int mmc_of_parse_voltage(struct device_node *np, u32 *mask)
 	int num_ranges, i;
 
 	voltage_ranges = of_get_property(np, "voltage-ranges", &num_ranges);
-	num_ranges = num_ranges / sizeof(*voltage_ranges) / 2;
 	if (!voltage_ranges) {
 		pr_debug("%pOF: voltage-ranges unspecified\n", np);
 		return 0;
 	}
+	num_ranges = num_ranges / sizeof(*voltage_ranges) / 2;
 	if (!num_ranges) {
 		pr_err("%pOF: voltage-ranges empty\n", np);
 		return -EINVAL;