commit b34ca601 upstream.

Ensure that if userspace supplies insufficient data to PTRACE_SETREGSET
to fill all the check pointed registers, the thread's old check pointed
registers are preserved.

Fixes: 9d3918f7 ("powerpc/ptrace: Enable support for NT_PPC_CVSX")
Fixes: 19cbcbf7 ("powerpc/ptrace: Enable support for NT_PPC_CFPR")
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>