scsi: acornscsi: Fix an error handling path in acornscsi_probe()

'ret' is known to be 0 at this point.  Explicitly return -ENOMEM if one of
the 'ecardm_iomap()' calls fail.

Link: https://lore.kernel.org/r/20200530081622.577888-1-christophe.jaillet@wanadoo.fr
Fixes: e95a1b65

 ("[ARM] rpc: acornscsi: update to new style ecard driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>