aic94xx: set an error code on failure

We recently did some cleanup here and now the static checkers notice
that there is a missing error code when ioremap() fails.  Let's set it
to -ENOMEM.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: James Bottomley <JBottomley@Odin.com>