That variable is useless, instead the variables specified_mode_num and specified_disp_id can cover all the situation.
For parameter -o, all three instances should work:

./testdisplay -o 21,4 only test the 4th mode on the connector with id 21.
./testdisplay -o 21   test all the mode lines on the connector wiht id 21.
./testdisplay -o ,4   the -o is ignored, just like -a.

Signed-off-by: Yi Sun <yi.sun@intel.com>