grub: fix extraction of AH and CF from get_target_operating_mode()
Review Request #87 - Created Aug. 26, 2015 and submitted
The logic was reversed.
Please see this for some discussion: http://f.osdev.org/viewtopic.php?p=161565&sid=fef9739a304d873c5e231a41a0c86b46#p161565
It seems that OpenSolaris GRUB did not have this bug.
Tested in a virtual machine with firmware returning either a success or an error for INT 15h, AX=EC00h, BL=3.