[Fix] Path mapping only once in storage backends (#2204)

* [Fix] Path mapping only once in storage backends

* Fix lint
Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

mmcv/fileio/file_client.py

@@ -74,7 +74,7 @@ class CephBackend(BaseStorageBackend):
         filepath = str(filepath)
         if self.path_mapping is not None:
             for k, v in self.path_mapping.items():
-                filepath = filepath.replace(k, v)
+                filepath = filepath.replace(k, v, 1)
         value = self._client.Get(filepath)
         value_buf = memoryview(value)
         return value_buf
@@ -129,7 +129,7 @@ class PetrelBackend(BaseStorageBackend):
         filepath = str(filepath)
         if self.path_mapping is not None:
             for k, v in self.path_mapping.items():
-                filepath = filepath.replace(k, v)
+                filepath = filepath.replace(k, v, 1)
         return filepath
 
     def _format_path(self, filepath: str) -> str: