dm: core: gracefully handle alias seq without of

Gracefully handle alias seq in the platform data rather than OF case.

Signed-off-by: Marcel Ziswiler <marcel@ziswiler.com>
diff --git a/include/dm/read.h b/include/dm/read.h
index 1c1bc37..3711386 100644
--- a/include/dm/read.h
+++ b/include/dm/read.h
@@ -923,8 +923,12 @@
 
 static inline int dev_read_alias_seq(const struct udevice *dev, int *devnump)
 {
+#if CONFIG_IS_ENABLED(OF_CONTROL)
 	return fdtdec_get_alias_seq(gd->fdt_blob, dev->uclass->uc_drv->name,
 				    dev_of_offset(dev), devnump);
+#else
+	return -ENOTSUPP;
+#endif
 }
 
 static inline int dev_read_u32_array(const struct udevice *dev,