xtensa: set proper error code for simdisk_setup()

Change error code to -ENOMEM from -EIO because
the error is related to memory allocating.

Signed-off-by: Chengguang Xu <cgxu519@gmail.com>
Message-Id: <1557066367-4783-2-git-send-email-cgxu519@gmail.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>