scsi: libsas: move bus_reset_handler() to target_reset_handler()

The bus reset handler is calling I_T Nexus reset, which logically is a
target reset as it need to specify both the initiator and the target.
So move it to target reset.

Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>