Fix swapped backup/heavy oom adj labels

The labels for the "backup" and "heavy" oom adj are swapped relative
to the ordering in DUMP_MEM_OOM_ADJ. Swap the order of the labels
to be consistent.

This should resolve an issue where meminfo mixes up heavy and backup
in the text-based report.

Change-Id: Idbc985c3080eada0945c21825659b031f1f7f2a5
Signed-off-by: Chris Phlipot <cphlipot@fb.com>