vfio/ccw: sort out physical vs virtual pointers usage

The ORB's interrupt parameter field is stored unmodified into the
interruption code when an I/O interrupt occurs. As this reflects
a real device, let's store the physical address of the subchannel
struct so it can be used when processing an interrupt.

Note: this currently doesn't fix a real bug, since virtual
addresses are identical to physical ones.

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
[EF: Updated commit message]
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
Link: https://lore.kernel.org/r/20221121165836.283781-2-farman@linux.ibm.com