KVM: s390: fix get_all_floating_irqs

This fixes a bug introduced with commit c05c4186 ("KVM: s390:
add floating irq controller").

get_all_floating_irqs() does copy_to_user() while holding
a spin lock. Let's fix this by filling a temporary buffer
first and copy it to userspace after giving up the lock.

Cc: <stable@vger.kernel.org> # 3.18+: 69a8d456

 KVM: s390: no need to hold...

Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>