Return the exported_program from transform to allow internal usage (#6210)

Summary:

It's mainly to make it easier to use internally...

Differential Revision: D64082731

Author: cccclai

backends/qualcomm/utils/utils.py

@@ -7,7 +7,7 @@
 import operator
 import warnings
 from collections import OrderedDict
-from typing import Callable, Dict, List, Set, Tuple
+from typing import Callable, Dict, FrozenSet, List, Set, Tuple
 
 import executorch.backends.qualcomm.python.PyQnnManagerAdaptor as PyQnnManagerAdaptor
 
@@ -290,9 +290,8 @@ def get_decomp_table() -> Dict[torch._ops.OperatorBase, Callable]:
 
 
 def _transform(
-    edge_program: ExportedProgram, custom_pass_config: Set[str] = None
-) -> None:
-    custom_pass_config = custom_pass_config or {}
+    edge_program: ExportedProgram, custom_pass_config: FrozenSet[str] = frozenset()
+) -> ExportedProgram:
     # currently ExirExportedProgram.transform does not accept
     # changes of input number which was caused by FoldQDQ
     # apply passes one by one here to avoid IR capture failure
@@ -322,6 +321,7 @@ def _transform(
         edge_program.graph_module,
     )
     edge_program._validate()
+    return edge_program
 
 
 def capture_program(