arm64: fault: avoid send SIGBUS two times

do_sea() calls arm64_notify_die() which will always signal
user-space. It also returns whether APEI claimed the external
abort as a RAS notification. If it returns failure do_mem_abort()
will signal user-space too.

do_mem_abort() wants to know if we handled the error, we always
call arm64_notify_die() so can always return success.

Signed-off-by: Dongjiu Geng <gengdongjiu@huawei.com>
Reviewed-by: James Morse <james.morse@arm.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>