vsh: Fix vshCompleter signature

The first argument passed to this function is vshControl *.
There's no need to use void pointer.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

tools/vsh.h

@@ -123,7 +123,8 @@ typedef struct _vshCmdOpt vshCmdOpt;
 typedef struct _vshCmdOptDef vshCmdOptDef;
 typedef struct _vshControl vshControl;
 
-typedef char **(*vshCompleter)(void *opaque, unsigned int flags);
+typedef char **(*vshCompleter)(vshControl *ctl,
+                               unsigned int flags);
 
 /*
  * vshCmdInfo -- name/value pair for information about command