s/finish/fini

For consistency.
diff --git a/src/hb-mutex-private.hh b/src/hb-mutex-private.hh
index 49ed10e..14bde31 100644
--- a/src/hb-mutex-private.hh
+++ b/src/hb-mutex-private.hh
@@ -134,7 +134,7 @@
   inline void init   (void) { hb_mutex_impl_init   (&m); }
   inline void lock   (void) { hb_mutex_impl_lock   (&m); }
   inline void unlock (void) { hb_mutex_impl_unlock (&m); }
-  inline void finish (void) { hb_mutex_impl_finish (&m); }
+  inline void fini (void) { hb_mutex_impl_finish (&m); }
 };