Fix compilation error

screen.o: In function `show_free_space':
/home/dsterba/_dev/mc-build/src/screen.c:783: undefined reference to
`mhl_mem_free'
/home/dsterba/_dev/mc-build/src/screen.c:784: undefined reference to
`mhl_str_dup'

Signed-off-by: David Sterba <dave@jikos.cz>

src/screen.c

@@ -780,8 +780,8 @@ show_free_space (WPanel *panel)
 	char rpath[PATH_MAX];
 
 	init_my_statfs ();
-	mhl_mem_free (old_cwd);
+	g_free (old_cwd);
-	old_cwd = mhl_str_dup (panel->cwd);
+	old_cwd = g_strdup (panel->cwd);
 
 	if (mc_realpath (panel->cwd, rpath) == NULL)
 	    return;