Hi Stefano,
Could you try this method? Can you extract the tar.gz and compile that instead of rpmbuild? It works for me.
# tar xfz nvidia-peer-memory_1.0.orig.tar.gz
# make
modify Makefile: replace $(DEPMOD) with depmod
# make install
# lsmod|grep -i nv
nvidia 8646656 0
drm 364544 5 ast,ttm,drm_kms_helper,nvidia
# insmod nv_peer_mem.ko
# lsmod|grep -i nv
nv_peer_mem 16384 0
nvidia 8646656 1 nv_peer_mem
ib_core 139264 14 rdma_cm,ib_cm,ib_sa,iw_cm,nv_peer_mem,mlx4_ib,mlx5_ib,ib_mad,ib_ucm,ib_iser,ib_umad,ib_uverbs,rdma_ucm,ib_ipoib
drm 364544 5 ast,ttm,drm_kms_helper,nvidia