checkpatch.conf: ignore imported sbcap *.asn files

Prepare to import files to library/sbcap, which we don't want to be
linted in Ia6743e0a3e7974a5f2dd3ecf74ec331f646f6bc2.

Change-Id: I3ab3253753d32a266bdaf32fb247c2c0139d40d3
1 file changed