ppc/ppc405_boards: Remove unnecessary NULL check

ppc/ppc405_boards: Remove unnecessary NULL check

This code is inside the "if (dinfo)" condition, so testing
again here whether it is NULL is unnecessary.

Fixes: dd59bcae7 (Don't size flash memory to match backing image)
Reported-by: Coverity (CID 1421917)
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200320155740.5342-1-philmd@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>