s390: trim ancient junk from copy_thread()

Setting and ->psw.addr in childregs of kernel thread is a rudiment of
the old kernel_thread()/kernel_execve() implementation.  Mainline hadn't
been using them since 2012.

And clarify the assigments to frame->sf.gprs - the array stores grp6..gpr15
values to be set by __switch_to(), so frame->sf.gprs[5] actually affects
grp11, etc.  Better spell that as frame->sf.gprs[11 - 6]...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
1 file changed