label extcon files

Bug: 199218084
Test: boot with those files labeled
09-09 10:39:55.703  1660  1660 W android.ui: type=1400 audit(0.0:6):
avc: denied { read } for name="name" dev="sysfs" ino=62812
scontext=u:r:system_server:s0 tcontext=u:object_r:sysfs_extcon:s0
tclass=file permissivei=0

Change-Id: Iba001f99cf9290f55f860382829c8ce74912f14c
1 file changed