tools: ynl: order building samples after generated code

Parallel builds of ynl:

  make -C tools/net/ynl/ -j 4

don't work correctly right now. samples get handled before
generated, so build of samples does not notice that protos.a
has changed. Order samples to be last.

Link: https://lore.kernel.org/r/20231129193622.2912353-4-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>