s390/vfio-ap: Fix no AP queue sharing allowed message written to kernel log

s390/vfio-ap: Fix no AP queue sharing allowed message written to kernel log

An erroneous message is written to the kernel log when either of the
following actions are taken by a user:

1. Assign an adapter or domain to a vfio_ap mediated device via its sysfs
   assign_adapter or assign_domain attributes that would result in one or
   more AP queues being assigned that are already assigned to a different
   mediated device. Sharing of queues between mdevs is not allowed.

2. Reserve an adapter or domain for the host device driver via the AP bus
   driver's sysfs apmask or aqmask attribute that would result in providing
   host access to an AP queue that is in use by a vfio_ap mediated device.
   Reserving a queue for a host driver that is in use by an mdev is not
   allowed.

In both cases, the assignment will return an error; however, a message like
the following is written to the kernel log:

vfio_ap_mdev e1839397-51a0-4e3c-91e0-c3b9c3d3047d: Userspace may not
re-assign queue 00.0028 already assigned to \
e1839397-51a0-4e3c-91e0-c3b9c3d3047d

Notice the mdev reporting the error is the same as the mdev identified
in the message as the one to which the queue is being assigned.
It is perfectly okay to assign a queue to an mdev to which it is
already assigned; the assignment is simply ignored by the vfio_ap device
driver.

This patch logs more descriptive and accurate messages for both 1 and 2
above to the kernel log:

Example for 1:
vfio_ap_mdev 0fe903a0-a323-44db-9daf-134c68627d61: Userspace may not assign
queue 00.0033 to mdev: already assigned to \
62177883-f1bb-47f0-914d-32a22e3a8804

Example for 2:
vfio_ap_mdev 62177883-f1bb-47f0-914d-32a22e3a8804: Can not reserve queue
00.0033 for host driver: in use by mdev

Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Link: https://lore.kernel.org/r/20250311103304.1539188-1-akrowiak@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>