fdtdec: only create phandle if caller wants it in fdtdec_add_reserved_memory()

The phandlep pointer returning the phandle to the caller is optional
and if it is not set when calling fdtdec_add_reserved_memory() it is
highly likely that the caller is not interested in a phandle to the
created reserved-memory area and really just wants that area added.

So just don't create a phandle in that case.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/fdtdec.h b/include/fdtdec.h
index e150975..696e0fd 100644
--- a/include/fdtdec.h
+++ b/include/fdtdec.h
@@ -1061,7 +1061,7 @@
  * @param basename	base name of the node to create
  * @param carveout	information about the carveout region
  * @param phandlep	return location for the phandle of the carveout region
- *			can be NULL
+ *			can be NULL if no phandle should be added
  * @return 0 on success or a negative error code on failure
  */
 int fdtdec_add_reserved_memory(void *blob, const char *basename,