ld-version: Drop the 4th and 5th version components

... making upstream development binutils snapshots work as expected,
e.g.:

$ mips64el-linux-ld --version
GNU ld (GNU Binutils) 2.20.1.20100303
[...]
$

Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: linux-kbuild@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12537/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>