print_edid: Fix a format string error

../hw/xfree86/ddc/print_edid.c:511:20: error: format specifies type 'unsigned short' but the argument has type 'int' [-Werror,-Wformat]
                   det_mon->type - DS_VENDOR);
                   ^~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>