iotests: Fix reference output for 059

It was broken by efaa7c4e when it dropped the device name "image"
from BB API.  Now this error message text is updated again, sync it up.
Signed-off-by: NFam Zheng <famz@redhat.com>
Message-id: 20170119130759.28319-3-famz@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

tests/qemu-iotests/059.out

@@ -2361,5 +2361,5 @@ Offset          Length          Mapped to       File
 0x140000000     0x10000         0x50000         TEST_DIR/iotest-version3-s003.vmdk
 
 === Testing afl image with a very large capacity ===
-qemu-img: Can't get size of device 'image': File too large
+qemu-img: Can't get image size 'TEST_DIR/afl9.IMGFMT': File too large
 *** done