Merge pull request #559 from Subv/mount_savedata

Services/FS: Return the correct error code when trying to mount a nonexistent savedata.

src/core/file_sys/errors.h

@@ -11,6 +11,7 @@ namespace FileSys {
 namespace ErrCodes {
 enum {
     NotFound = 1,
+    SaveDataNotFound = 1002,
 };
 }