Simplify reporting from init_gpu
makeGpuUsageReport reports whether the usage was selected by the user
or not, and has been run before we call init_gpu.
In any case, the reporting from init_gpu should only happen if mygpu
contains an invalid value, which should never happen so late in the
code, ie after all the previous consistency checks. Knowing whether
the user selected the GPUs or not doesn't help much, and that
information is available from makeGpuUsageReport, anyway.
Change-Id: I1b701dceb4f4c5ee62175827b6a70bb134b0f66a