Fix a oops in _scsih_sas_device_remove.  The driver was attempting to
delete a object from the sas_device link list when the object was not
present.

Added sanity check for sas_device NULL dereference.
before deleting sas_device now driver will search device in list then
only it will follow device removal.
Signed-off-by: NKashyap Desai <kashyap.desai@lsi.com>
Signed-off-by: NJames Bottomley <James.Bottomley@suse.de>