powerpc/syscall: Change condition to check MSR_RI

In system_call_exception(), MSR_RI also needs to be checked on 8xx.
Only booke and 40x doesn't have MSR_RI.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/67820fada8dd6a8fe9d7b666f175d4cc9d8de87e.1612796617.git.christophe.leroy@csgroup.eu