mk: fix linker script when re-building

mk: fix linker script when re-building

The linker script is generated by simply finding all libraries in
RTE_OUTPUT/lib.

The issue shows up when re-building the DPDK, hence already having a
linker script in that directory, resulting in the linker script
including itself.

That does not play well with the linker.

Simply filtering the linker script from all the found libraries solves
the problem.

Fixes: 948fd64befc3 ("mk: replace the combined library with a linker script")

Signed-off-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>
Acked-by: Panu Matilainen <pmatilai@redhat.com>