Fix multiple lun file USB mounting

Both the incorrect mount point and the incorrect lun file were being
passed as the second storage volume.

Change-Id: If9c7d92d1992ec022a2c89a82b2ea05c9150d635
diff --git a/partitionmanager.cpp b/partitionmanager.cpp
index b947d43..9d8c273 100644
--- a/partitionmanager.cpp
+++ b/partitionmanager.cpp
@@ -1573,7 +1573,6 @@
 int TWPartitionManager::usb_storage_enable(void) {
 	int has_dual, has_data_media;
 	char lun_file[255];
-	string ext_path;
 	bool has_multiple_lun = false;
 
 	DataManager::GetValue(TW_HAS_DATA_MEDIA, has_data_media);
@@ -1608,9 +1607,10 @@
 		if (Mount1) {
 			if (!Open_Lun_File(Mount1->Mount_Point, lun_file))
 				return false;
+			sprintf(lun_file, CUSTOM_LUN_FILE, 1);
 			Mount2 = Find_Next_Storage(Mount1->Mount_Point, "/data");
 			if (Mount2) {
-				Open_Lun_File(ext_path, lun_file);
+				Open_Lun_File(Mount2->Mount_Point, lun_file);
 			}
 		} else {
 			LOGERR("Unable to find storage partition to mount to USB\n");