Fix to return a negative error code from the kthread_run() error
handling case instead of 0, as done elsewhere in this function.

Fixes: cdd5de50 ("soc: ti: Add wkup_m3_ipc driver")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>