driver: bcmdhd: do not allow hang thread after cleanup

do not allow scheduling hang thread after cleanup
is done.

Bug 1210849
Bug 1205910
Bug 1163014

Change-Id: Idc5f9fd6a3d210843f1168e57ceef107599d5789
Signed-off-by: Mursalin Akon <makon@nvidia.com>
Reviewed-on: http://git-master/r/189721
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Matthew Pedro <mapedro@nvidia.com>
Reviewed-by: Allen Martin <amartin@nvidia.com>