scsi_dh_alua: uninitialized variable in alua_rtpg()

It's possible to use "err" without initializing it.  If it happens to be
a 2 which is SCSI_DH_RETRY then that could cause a bug.  Bart Van Assche
pointed out that we should probably re-initialize it for every iteration
through the retry loop.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Hannes Reinicke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <jejb@linux.vnet.ibm.com>