Fix incorrect quota size reported

This PR partially re-introduces the logic attempting to get the free space for a specific path.

The code before this would incorrectly always return the free space of `/` on non-Windows, instead of the actual mounted path's free space.

Duplicati/Library/Utility/Utility.cs

@@ -2104,7 +2104,7 @@ namespace Duplicati.Library.Utility
                 }
                 else if (!OperatingSystem.IsWindows())
                 {
-                    var driveInfo = new DriveInfo(root);
+                    var driveInfo = new DriveInfo(path);
                     if (driveInfo.TotalSize > 0)
                         return (driveInfo.AvailableFreeSpace, driveInfo.TotalSize);
                 }