samples/bpf: Fix compilation issue in redirect dummy program

Fix compilation error below:

$ make samples/bpf/

LLVM ERROR: 'xdp_redirect_dummy' label emitted multiple times to
assembly file
make[1]: *** [samples/bpf/xdp_redirect_kern.o] Error 1
make: *** [samples/bpf/] Error 2

Fixes: 306da4e6 ("samples/bpf: xdp_redirect load XDP dummy prog on TX device")
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>