[OpenMP-RT] Fix debug string for NVPTX runtime library

https://reviews.llvm.org/D42757

The method ThreadsInTeam is used to determine the number of threads to be used in a parallel region under SPMD mode (see line 127 of supporti.h in libomptarget/deviceRTLs/nvptx/src/). This patch fixes the corresponding debug print upon initialization of the kernel in SPMD mode.

llvm-svn: 323978