Cleaned up use of substr() to get interface's base name.

Bug: 31527442

Test: make at top-level. hidl_test passes.

Change-Id: Ia940a421599dc158e26fb7ea481abeab32620f65
diff --git a/Interface.cpp b/Interface.cpp
index 0fe7e87..a5d3c9b 100644
--- a/Interface.cpp
+++ b/Interface.cpp
@@ -58,8 +58,7 @@
 }
 
 std::string Interface::getBaseName() const {
-    // cut off the leading 'I'.
-    return localName().substr(1);
+    return fqName().getInterfaceBaseName();
 }
 
 std::string Interface::getCppType(StorageMode mode,