zio-sys: delay copying current_ctrl to block->ctrl

This is a potentially incompatible change: if your driver fills
attributes in the input block at raw_io() time, it won't work any more.
You should fill chan->current_ctrl instead, which will be visible
as a binary blob in sysfs soon.

Moving the memcpy() to a later point doesn't change overhead.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Federico Vaga <federico.vaga@gmail.com>