linux-user: Correct type for BLKSSZGET

The BLKSSZGET ioctl takes an argument which is a pointer to an int.
We were incorrectly declaring it to take a pointer to a long, which
meant that we would incorrectly write to memory which we should not
if the guest is a 64-bit architecture.

In particular, kpartx uses this ioctl to write to an int on the
stack, which tends to result in it crashing immediately.

Reported-by: Chanho Park <chanho61.park@samsung.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>