usb: ehci: mxs: Use regulator_set_enable_if_allowed()

Since commit 4fcba5d556b4 ("regulator: implement basic reference
counter") the return value of regulator_set_enable() may be EALREADY or
EBUSY for fixed/GPIO regulators.

Switch to using the more relaxed regulator_set_enable_if_allowed() to
continue if regulator already was enabled or disabled.

This fixes the following error when running the 'ums' command:

=> ums 0 mmc 0
UMS: LUN 0, dev mmc 0, hwpart 0, sector 0x0, count 0xece000
Error enabling VBUS supply
g_dnl_register: failed!, error: -114
g_dnl_register failed

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/drivers/usb/host/ehci-mxs.c b/drivers/usb/host/ehci-mxs.c
index 092c79f..ddf7cc2 100644
--- a/drivers/usb/host/ehci-mxs.c
+++ b/drivers/usb/host/ehci-mxs.c
@@ -236,9 +236,9 @@
 		debug("%s: No vbus supply\n", dev->name);
 
 	if (!ret && priv->vbus_supply) {
-		ret = regulator_set_enable(priv->vbus_supply,
-					   (type == USB_INIT_DEVICE) ?
-					   false : true);
+		ret = regulator_set_enable_if_allowed(priv->vbus_supply,
+						      (type == USB_INIT_DEVICE) ?
+						      false : true);
 		if (ret) {
 			puts("Error enabling VBUS supply\n");
 			return ret;
@@ -265,7 +265,7 @@
 
 #if CONFIG_IS_ENABLED(DM_REGULATOR)
 	if (priv->vbus_supply) {
-		ret = regulator_set_enable(priv->vbus_supply, false);
+		ret = regulator_set_enable_if_allowed(priv->vbus_supply, false);
 		if (ret) {
 			puts("Error disabling VBUS supply\n");
 			return ret;