Fix erroneous section label in oatdump

At some point the 7th root in an images root table became
kSpecialRoots. The stringify array in oatdump was not updated however
causing it to be incorrectly labeled as kClassLoader.

Test: m oatdump
Test: oatdump --image=/system/frameworks/boot.oat
Change-Id: I71dd1223704fc8bb759f43f599fad19119a76782