Replace usages of FROM_I2C_SLAVE() with QOM cast macro.
Rename the parent field. Reuse the type constant in z2_init().
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
[AF: Use TYPE_AER915 in z2_init() too]
Signed-off-by: Andreas Färber <afaerber@suse.de>