Log error on io buffer allocation

Currently it just exits silently.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/memory.c b/memory.c
index f67dd6d..d075c35 100644
--- a/memory.c
+++ b/memory.c
@@ -145,6 +145,9 @@
 		ret = 1;
 	}
 
+	if (ret)
+		td_verror(td, ENOMEM, "iomem allocation");
+
 	return ret;
 }