test/dm/core.c: Make pre-reloc test use pre-reloc struct

LLVM 3.5 noted:
test/dm/core.c:41:35: warning: unused variable 'test_pdata_pre_reloc' [-Wunused-const-variable]
static const struct dm_test_pdata test_pdata_pre_reloc = {

And the correct fix here is that the driver_info_pre_reloc test should
use the test_pdata_pre_reloc not test_pdata_manual variable

Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>