Bluetooth: Send pairing cancel intent only if pairing in progress

This patch sends pairing cancel intent on acl disconnetion only if
pairing is in progress. Without this patch, in case there was an
ongoing pairing while acl disconnect is received for some other
device, ongoing pairing was getting cancelled un-intentionally due
to side-effects caused by dbff9ae0ebdcdf63db6c125331002dbb6f50f953

Change-Id: I859f79a8b7f196fe7617419dbbd6284a47228700
CRs-Fixed: 508911