[nrf fromlist] devicetree: Fix MTD macro for subpartitions

The DT_MTD_FROM_FIXED_SUBPARTITION must go one level more than the
DT_MTD_FROM_FIXED_PARTITION counterpart.

Upstream PR #: 96808

Signed-off-by: Tomasz Chyrowicz <[email protected]>

Author: tomchy

include/zephyr/devicetree/fixed-partitions.h

@@ -160,7 +160,7 @@ extern "C" {
  */
 #define DT_MTD_FROM_FIXED_SUBPARTITION(node_id)                                                    \
 	COND_CODE_1(DT_NODE_EXISTS(DT_MEM_FROM_FIXED_SUBPARTITION(node_id)),                       \
-		    (DT_PARENT(DT_MEM_FROM_FIXED_SUBPARTITION(node_id))), (DT_GPARENT(node_id)))
+	     (DT_PARENT(DT_MEM_FROM_FIXED_SUBPARTITION(node_id))), (DT_GPARENT(DT_PARENT(node_id))))
 
 /**
  * @brief Get the absolute address of a fixed subpartition