selftests: powerpc: Fix warning for security subdir

[Michael Ellerman]

On Mon, 2018-10-22 at 12:09:26 UTC, Joel Stanley wrote:
> typing 'make' inside tools/testing/selftests/powerpc gave a build
> warning:
> 
> BUILD_TARGET=tools/testing/selftests/powerpc/security; mkdir -p $BUILD_TARGET; make OUTPUT=$BUILD_TARGET -k -C security all
> make[1]: Entering directory 'tools/testing/selftests/powerpc/security'
> ../../lib.mk:20: ../../../../scripts/subarch.include: No such file or directory
> make[1]: *** No rule to make target '../../../../scripts/subarch.include'.
> make[1]: Failed to remake makefile '../../../../scripts/subarch.include'.
> 
> The build is one level deeper than lib.mk thinks it is. Set top_srcdir
> to set things straight.
> 
> Note that the test program is still built.
> 
> Signed-off-by: Joel Stanley <joel at jms.id.au>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/a0aebae07f211c05d64be886e56d35

cheers