Fixed gcc warning

Fixed gcc warning

In cups/dest.c:

    dest.c:1830:21: warning: ‘%s’ directive argument is null [-Wformat-overflow=]
     1733 |       DEBUG_printf(("1cupsGetNamedDest: Using name=\"%s\"...", name));
	  |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is really true, and gcc was smart enough to deduct it from context.
Obviously, we meant to print dest_name here.