patch 8.2.0774: t_TI and t_TE are output when using 'visualbell'

Problem:    t_TI and t_TE are output when using 'visualbell'. (Dominique
            Pelle)
Solution:   Do not change the terminal mode for a short sleep.  Do not output
            t_TI and t_TE when switching to/from TMODE_SLEEP. Make tmode an
            enum.
diff --git a/src/os_vms.c b/src/os_vms.c
index 96fbc17..b8ad788 100644
--- a/src/os_vms.c
+++ b/src/os_vms.c
@@ -112,7 +112,7 @@
 }
 
     void
-mch_settmode(int tmode)
+mch_settmode(tmode_T tmode)
 {
     int	status;