scsi: aha1740: Fix an errro handling path in aha1740_probe()

If 'dma_map_single()' fails, the ref counted 'shpnt' will be decremented
twice because 'scsi_host_put()' is called in the if block, and in the error
handling path.

Axe one of these calls.

Link: https://lore.kernel.org/r/20200228215948.7473-1-christophe.jaillet@wanadoo.fr


Fixes: 1dc09e12 ("scsi: aha1740: stop using scsi_unregister")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>