The load_image() function is deprecated, as it does not let the
caller specify how large the buffer to read the file into is.
Instead use load_image_size().

While we are converting this code, add an error-check
for read failure.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-id: 20181130151712.2312-5-peter.maydell@linaro.org