Return -ENOMEM if the allocation fails.  Don't return success.

Fixes: 6598b91b ("spi: spi.c: Convert statistics to per-cpu u64_stats_t")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/Yqh6bdNYO2XNhPBa@kiliSigned-off-by: NMark Brown <broonie@kernel.org>