recovery: switch to fs_mgr_read_fstab_default()

fs_mgr_read_fstab_default() is now aware of recovery mode so it's ok to
switch to this new API.

Bug: 35811655
Test: recovery boot sailfish
Change-Id: I1025b606fd96e74a893ae99cefc1da01e4b27a23
(cherry picked from commit 84a06485a9)

roots.cpp

@@ -44,9 +44,9 @@ void load_volume_table()
     int i;
     int ret;
 
-    fstab = fs_mgr_read_fstab_with_dt("/etc/recovery.fstab");
+    fstab = fs_mgr_read_fstab_default();
     if (!fstab) {
-        LOG(ERROR) << "failed to read /etc/recovery.fstab";
+        LOG(ERROR) << "failed to read default fstab";
         return;
     }