Update hftest.sh to pass correct argument to hftest.py for FVP.

This was changed in hftest.py in
https://hafnium-review.googlesource.com/c/hafnium/+/8560 but not
updated here.

Change-Id: I795bac11aed125fc47606e26d8cad2d5803cfe9c
1 file changed