hw/sd/milkymist-memcard: Reset SD card on controller reset

hw/sd/milkymist-memcard: Reset SD card on controller reset

Since milkymist-memcard is still using the legacy SD card API,
the SD card created by sd_init() is not plugged into any bus.
This means that the controller has to reset it manually.

Failing to do this mostly didn't affect the guest since the
guest typically does a programmed SD card reset as part of
its SD controller driver initialization, but meant that
migration failed because it's only in sd_reset() that we
set up the wpgrps_size field.

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 1515506513-31961-3-git-send-email-peter.maydell@linaro.org