ppc/xive: Fix PHYS NSR ring matching

ppc/xive: Fix PHYS NSR ring matching

Test that the NSR exception bit field is equal to the pool ring value,
rather than any common bits set, which is more correct (although there
is no practical bug because the LSI NSR type is not implemented and
POOL/PHYS NSR are encoded with exclusive bits).

Fixes: 4c3ccac636 ("pnv/xive: Add special handling for pool targets")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Reviewed-by: Michael Kowal <kowal@linux.ibm.com>
Reviewed-by: Caleb Schlossin <calebs@linux.ibm.com>
Tested-by: Gautam Menghani <gautam@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20250512031100.439842-7-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>