Add the missing extcon directory to maintain them.  When using
get_maintainer.pl, the result should include the correct maintainer
information.
Signed-off-by: NChanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>