staging: prima: Actually update to CAF LNX.LA.3.5.1.1-07000-8x74.0

The last update was a 'git merge' on the prima repository, which
didn't reflect all the changes between the old and the above tag
for some reason.
Fix this by checking out the above tag while
preserving local modifitions.

This resolves the wifi tethering issue for everyone.
Bug: CYAN-4312

Change-Id: Iedd36005b01f6df8eff44af32fbf58b18169b2ae