sysreset: use syscon_regmap_lookup_by_phandle

Use the new function syscon_regmap_lookup_by_phandle()
to simplify the code.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/drivers/sysreset/sysreset_syscon.c b/drivers/sysreset/sysreset_syscon.c
index 3450640..3fb39b9 100644
--- a/drivers/sysreset/sysreset_syscon.c
+++ b/drivers/sysreset/sysreset_syscon.c
@@ -36,20 +36,9 @@
 int syscon_reboot_probe(struct udevice *dev)
 {
 	struct syscon_reboot_priv *priv = dev_get_priv(dev);
-	int err;
-	u32 phandle;
-	ofnode node;
 
-	err = ofnode_read_u32(dev_ofnode(dev), "regmap", &phandle);
-	if (err)
-		return err;
-
-	node = ofnode_get_by_phandle(phandle);
-	if (!ofnode_valid(node))
-		return -EINVAL;
-
-	priv->regmap = syscon_node_to_regmap(node);
-	if (!priv->regmap) {
+	priv->regmap = syscon_regmap_lookup_by_phandle(dev, "regmap");
+	if (IS_ERR(priv->regmap)) {
 		pr_err("unable to find regmap\n");
 		return -ENODEV;
 	}