sparc32: Pass task_struct to schedule_tail() in ret_from_fork

We have to pass task_struct of previous process to function
schedule_tail(). Currently in ret_from_fork previous thread_info
is passed:

switch_to: mov %g6, %g3 /* previous thread_info in g6 */

ret_from_fork: call    schedule_tail
                mov    %g3, %o0 /* previous thread_info is passed */

void schedule_tail(struct task_struct *prev);

Signed-off-by: Tkhai Kirill <tkhai@yandex.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>