mailbox: k3-sec-proxy: fix error handling for missing scfg in FDT

The wrong field was checked.

Fixes: f9aa41023bd9 ("mailbox: Introduce K3 Secure Proxy Driver")
Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Reviewed-by: Nishanth Menon <nm@ti.com>
diff --git a/drivers/mailbox/k3-sec-proxy.c b/drivers/mailbox/k3-sec-proxy.c
index 8158084..2707261 100644
--- a/drivers/mailbox/k3-sec-proxy.c
+++ b/drivers/mailbox/k3-sec-proxy.c
@@ -326,7 +326,7 @@
 	}
 
 	spm->scfg = devfdt_get_addr_name(dev, "scfg");
-	if (spm->rt == FDT_ADDR_T_NONE) {
+	if (spm->scfg == FDT_ADDR_T_NONE) {
 		dev_err(dev, "No reg property for Secure Cfg base\n");
 		return -EINVAL;
 	}