powerpc/traps: fix recoverability of machine check handling on book3s/32

powerpc/traps: fix recoverability of machine check handling on book3s/32

Looks like book3s/32 doesn't set RI on machine check, so
checking RI before calling die() will always be fatal
allthought this is not an issue in most cases.

Fixes: 4f1bd7f6d661 ("powerpc: Machine check interrupt is a non-maskable interrupt")
Fixes: 56cd061a819a ("powerpc/traps: restore recoverability of machine_check interrupts")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: stable@vger.kernel.org
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>