You CAN, but the experience will not be very enjoyable even on the lowest settings
HD5450 can play COD ghost, but at very low settings and certainly not at 1920x1080, maybe 1280x800. I have an R9 270 myself, set everything on max and it takes like 1.2-1.8gb of the VRAM.
6GB ram is problematic for Call of Duty Ghost since that game is completely broken. Even when you start the game it hogs 2gb from the start. You must get a RAM patch fix if you don't want it to crash every 15 mins. Otherwise your experience will be awful.
A bit of warning playing at low settings. COD has very bad texture mapping, so if you play at low, the game is really blurry, lots of fuzzy edges. Not recommended.