MN10300: Fix ret_from_kernel_thread

MN10300: Fix ret_from_kernel_thread

ret_from_kernel_thread needs to set A2 to the thread_info pointer before
jumping to syscall_exit.

Without this, we never correctly start userspace.

This was caused by the rejuggling of the fork/exec paths in commit
ddf23e87a804 ("mn10300: switch to saner kernel_execve() semantics")

Reported-by: Ken Cox <[email protected]>
Signed-off-by: David Howells <[email protected]>
Acked-by: Ken Cox <[email protected]>
Acked-by: Al Viro <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>