smbd: Simplify dptr_ReadDirName()

smbd: Simplify dptr_ReadDirName()

While trying to understand the ReadDirName() at the end of
dptr_ReadDirName() in a code path that was supposed to be just a
"stat"-style readdir with a non-wcard mask I came to the conclusion
that this was there to find dptr->wcard with a mangled
name. get_real_filename_at() already takes care of name mangling, so I
think I could eliminate a source of confusion by using it.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>