tile: array underflow in setup_maxnodemem()

tile: array underflow in setup_maxnodemem()

commit 637f23abca87d26e091e0d6647ec878d97d2c6cd upstream.

My static checker correctly complains that we should have a lower bound
on "node" to prevent an array underflow.

Fixes: 867e359b97c9 ("arch/tile: core support for Tilera 32-bit chips.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
[bwh: Backported to 3.2: keep maxnodemem_mb as long]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>