misc: ub251xb: Fix use of CONFIG_IS_ENABLED on DM_REGULATOR

The DM_REGULATOR symbol has SPL counterpart in:
  drivers/power/regulator/Kconfig:config SPL_DM_REGULATOR
Use CONFIG_IS_ENABLED() macro to match on the correct
variant depending on the build stage.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/misc/usb251xb.c b/drivers/misc/usb251xb.c
index a78ad18..92e92ba 100644
--- a/drivers/misc/usb251xb.c
+++ b/drivers/misc/usb251xb.c
@@ -334,7 +334,7 @@
 	struct usb251xb *hub = dev_get_priv(dev);
 	int err;
 
-	if (IS_ENABLED(CONFIG_DM_REGULATOR) && hub->vdd) {
+	if (CONFIG_IS_ENABLED(DM_REGULATOR) && hub->vdd) {
 		err = regulator_set_enable(hub->vdd, true);
 		if (err)
 			return err;
@@ -391,7 +391,7 @@
 		return err;
 	}
 
-	if (IS_ENABLED(CONFIG_DM_REGULATOR)) {
+	if (CONFIG_IS_ENABLED(DM_REGULATOR)) {
 		err = device_get_supply_regulator(dev, "vdd-supply",
 						  &hub->vdd);
 		if (err && err != -ENOENT) {