linux-user: Correct type for LOOP_GET_STATUS{,64} ioctls

The LOOP_GET_STATUS and LOOP_GET_STATUS64 ioctls were incorrectly
defined as IOC_W rather than IOC_R, which meant we weren't
correctly copying the information back from the kernel to the guest.
The loop_info64 structure definition was also missing a member
and using the wrong type for several 32-bit fields.

In particular, this meant that "kpartx -d image.img" didn't work
and "losetup -a" behaved strangely. Correct the ioctl type definitions.

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>