linux-headers/asm is a symlink generated during configure.  It should not,
therefore be committed to git, nor show up in git diffs and the like.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>