mem: fix division by zero in no-NUMA mode

When RTE_EAL_NUMA_AWARE_HUGEPAGES is set to "n", not all memtypes
will be valid, because we skip some due to not supporting other
NUMA nodes, leading to a division by zero error down the line
because the necessary memtype fields weren't populated.

Fix it by limiting number of memtypes to number of memtypes we
have actually created.

Fixes: 1dd342d0fdc4 ("mem: improve segment list preallocation")
Cc: stable@dpdk.org
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Tested-by: David Hunt <david.hunt@intel.com>