[libc][obvious] Changed incorrect type (#143780)

After changing mbstate_t to mbstate we forgot to change the
character_converter files to reflect it.

Co-authored-by: Sriya Pratipati <sriyap@google.com>

libc/src/__support/wchar/character_converter.cpp

@@ -16,7 +16,7 @@
 namespace LIBC_NAMESPACE_DECL {
 namespace internal {
 
-CharacterConverter::CharacterConverter(mbstate_t *mbstate) { state = mbstate; }
+CharacterConverter::CharacterConverter(mbstate *mbstate) { state = mbstate; }
 
 bool CharacterConverter::isComplete() {}
 

libc/src/__support/wchar/character_converter.h

@@ -19,10 +19,10 @@ namespace internal {
 
 class CharacterConverter {
 private:
-  mbstate_t *state;
+  mbstate *state;
 
 public:
-  CharacterConverter(mbstate_t *mbstate);
+  CharacterConverter(mbstate *mbstate);
 
   bool isComplete();