Fix last sector write on sd card
When writing the last sector of an SD card using WRITE_MULTIPLE_BLOCK
QEmu throws an error saying that we've run off the end, and leaves
itself in the wrong state.
Tested on ARM Vexpress model.
Signed-off-by: Dr. David Alan Gilbert <david.gilbert@linaro.org>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>