I don't have an answer (yet), but I have the same problem, also on a new Samsung S5 - and also stuck at exactly 93%.
It's not a matter of uninstalling, because it hasn't been installed yet. I did try cancelling and restarting the download a couple of times, but always stops at 93% (24.02MB). I checked, and have plenty of space, so no issue there.
Must be some weird combo of the S5 and Facebook app?