Fix modules installation directory

While building zfs modules with kernel, compiled from deb.src, packaging process ends up installing modules in the wrong place. It installs them into
/tmp/zfs-build-builduser-zbZBpB9A/BUILDROOT/zfs-kmod-0.6.3-125_g88904bb.x86_64/lib/modules/3.16.5/
but debian (and packaging process) is looking for them in /lib/modules/3.16-3-amd64. So, packaging fails with
Processing files: kmod-zfs-3.16-3-amd64-0.6.3-125_g88904bb.x86_64
error: Directory not found: /tmp/zfs-build-builduser-zbZBpB9A/BUILDROOT/zfs-kmod-0.6.3-125_g88904bb.x86_64/lib/modules/3.16-3-amd64/extra
error: Directory not found: /tmp/zfs-build-builduser-zbZBpB9A/BUILDROOT/zfs-kmod-0.6.3-125_g88904bb.x86_64/lib/modules/3.16-3-amd64/extra/zfs