s390/vfio-ap: unpin pages on gisc registration failure

s390/vfio-ap: unpin pages on gisc registration failure

In the vfio_ap_irq_enable function, after the page containing the
notification indicator byte (NIB) is pinned, the function attempts
to register the guest ISC. If registration fails, the function sets the
status response code and returns without unpinning the page containing
the NIB. In order to avoid a memory leak, the NIB should be unpinned before
returning from the vfio_ap_irq_enable function.

Co-developed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Fixes: 783f0a3ccd79 ("s390/vfio-ap: add s390dbf logging to the vfio_ap_irq_enable function")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20231109164427.460493-2-akrowiak@linux.ibm.com
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>