vold: replacing fs_mgr_read_fstab() with fs_mgr_read_fstab_default()

The original default /fstab.{ro.hardware} might be moved to /vendor/etc/.
or /odm/etc/. Use the new API to get the default fstab instead of using
the hard-coded /fstab.{ro.hardware}.

Bug: 35811655
Test: boot marlin with /vendor/etc/fstab.marlin
Change-Id: I92d6aefe6ff3433b7d1a671358d990bb7b1f2150
diff --git a/main.cpp b/main.cpp
index 6754b0a..c106af9 100644
--- a/main.cpp
+++ b/main.cpp
@@ -215,10 +215,9 @@
 }
 
 static int process_config(VolumeManager *vm, bool* has_adoptable) {
-    std::string path(android::vold::DefaultFstabPath());
-    fstab = fs_mgr_read_fstab(path.c_str());
+    fstab = fs_mgr_read_fstab_default();
     if (!fstab) {
-        PLOG(ERROR) << "Failed to open default fstab " << path;
+        PLOG(ERROR) << "Failed to open default fstab";
         return -1;
     }