video: simple_panel: use regulator_set_enable_if_allowed

With the commit 4fcba5d556b4 ("regulator: implement basic reference
counter") the return value of regulator_set_enable may be EALREADY or
EBUSY for fixed/gpio regulators and may be further expanded on all
regulators.

Change to use the more relaxed regulator_set_enable_if_allowed to
continue if regulator already was enabled or disabled.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
diff --git a/drivers/video/simple_panel.c b/drivers/video/simple_panel.c
index 6a6473e..efb122b 100644
--- a/drivers/video/simple_panel.c
+++ b/drivers/video/simple_panel.c
@@ -114,11 +114,11 @@
 	const u32 dsi_data = dev_get_driver_data(dev);
 	int ret;
 
-	if (CONFIG_IS_ENABLED(DM_REGULATOR) && priv->reg) {
-		debug("%s: Enable regulator '%s'\n", __func__, priv->reg->name);
-		ret = regulator_set_enable(priv->reg, true);
-		if (ret)
-			return ret;
+	ret = regulator_set_enable_if_allowed(priv->reg, true);
+	if (ret && ret != -ENOSYS) {
+		debug("%s: failed to enable regulator '%s' %d\n",
+		      __func__, priv->reg->name, ret);
+		return ret;
 	}
 
 	switch (dsi_data) {