selftests/seccomp: powerpc: Fix seccomp return value testing

On powerpc, the errno is not inverted, and depends on ccr.so being
set. Add this to a powerpc definition of SYSCALL_RET_SET().

Co-developed-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Link: https://lore.kernel.org/linux-kselftest/20200911181012.171027-1-cascardo@canonical.com/
Fixes: 5d83c2b3

 ("selftests/seccomp: Add powerpc support")
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/lkml/20200912110820.597135-13-keescook@chromium.org


Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>