fpga: of-fpga-region: Fail if any bridge is missing

When parsing the region bridge list from the "fpga-bridges" device tree
property, the of-fpga-region driver will silently ignore bridges which fail
to be obtained, for example due to a missing bridge driver or invalid
phandle.

This can lead to hardware issues if a region bridge stays coupled when
partial programming is performed.

Fail if any of the bridges specified in "fpga-bridges" cannot be obtained.

Signed-off-by: Romain Gantois <[e-mail]>
Link: https://lore.kernel.org/r/202[e-mail]
Reviewed-by: Xu Yilun <[e-mail]>
Signed-off-by: Xu Yilun <[e-mail]>

drivers/fpga/of-fpga-region.c

···
  * done with the bridges.
  *
  * Return: 0 for success (even if there are no bridges specified)
- * or -EBUSY if any of the bridges are in use.
+ * or an error code if any of the bridges are not available.
  */
 static int of_fpga_region_get_bridges(struct fpga_region *region)
 {
···
 						 &region->bridge_list);
 		of_node_put(br);
 
-		/* If any of the bridges are in use, give up */
-		if (ret == -EBUSY) {
+		/* If any of the bridges are not available, give up */
+		if (ret) {
 			fpga_bridges_put(&region->bridge_list);
-			return -EBUSY;
+			return ret;
 		}
 	}