hw/char/exynos4210_uart: Fix crash on trying to load VM state

hw/char/exynos4210_uart: Fix crash on trying to load VM state

The exynos4210_uart_post_load() function assumes that it is passed
the Exynos4210UartState, but it has been attached to the
VMStateDescription for the Exynos4210UartFIFO type.  The result is a
SIGSEGV when attempting to load VM state for any machine type
including this device.

Fix the bug by attaching the post-load function to the VMSD for the
Exynos4210UartState.  This is the logical place for it, because the
actions it does relate to the entire UART state, not just the FIFO.

Thanks to the bug reporter @TrungNguyen1909 for the clear bug
description and the suggested fix.

Fixes: c9d3396d80fe7ece9b
   ("hw/char/exynos4210_uart: Implement post_load function")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/638
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20220120151648.433736-1-peter.maydell@linaro.org