kdebug: cannot run interpreter if kp_probe_init return failure

Oded report a panic on powerpc machine:

...
> Instruction dump:
> 419e0024 88030000 2f800000 409e0148 88180000 2f800000 409e011c 3b200000
> 3b000000 3f40f1ec 3ac00000 813a93a0 <83c90000> 7f89f000 419e00c0 3b5a93a0
> ---[ end trace b87e7dec14e55ffe ]---
>
> cannot lookup ftrace_events in kallsyms
> Kernel panic - not syncing: Fatal exception
> Rebooting in 5 seconds..

Obviously there missed a return value check for kp_probe_init, fix it.

Reported-by: Oded Gabbay <ogabbay@advaoptical.com>
Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>