scsi_dh_alua: call alua_rtpg() if stpg fails

If the call to SET TARGET PORT GROUPS fails we have no idea what
state the array is left in, so we need to issue a call to
REPORT TARGET PORT GROUPS in these cases.

Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>