target/ppc/mmu_common: Fix SRR1/MSR error code on Book-E

target/ppc/mmu_common: Fix SRR1/MSR error code on Book-E

Book-E architecture does not set the error code in 31:27 bits
of SRR1, but instead uses these bits for custom fields such
as GS (Guest Supervisor).

Wrongly setting these fields will result in QEMU crashes
when attempting to execute not executable code due to the attempts
to use Guest Supervisor mode.

Cc: "Cédric Le Goater" <clg@kaod.org>
Cc: Daniel Henrique Barboza <danielhb413@gmail.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Greg Kurz <groug@kaod.org>
Cc: qemu-ppc@nongnu.org
Cc: qemu-devel@nongnu.org
Cc: qemu-stable@nongnu.org
Signed-off-by: Vitaly Cheptsov <cheptsov@ispras.ru>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20220121093107.15478-1-cheptsov@ispras.ru>
Signed-off-by: Cédric Le Goater <clg@kaod.org>