hw/intc/arm_gicv3: Fix APxR<n> register dispatching

hw/intc/arm_gicv3: Fix APxR<n> register dispatching

There was a nasty flip in identifying which register group an access is
targeting. The issue caused spuriously raised priorities of the guest
when handing CPUs over in the Jailhouse hypervisor.

Cc: qemu-stable@nongnu.org
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Message-id: 28b927d3-da58-bce4-cc13-bfec7f9b1cb9@siemens.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>