[BUGFIX] Fix invalid global for getData hooks

Replace the invalid usage of $TYPO3_CONF_VARS with
$GLOBALS['TYPO3_CONF_VARS'] for getting the hook
configuration in ContentObjectRenderer::getData().

Resolves: #50606
Releases: 6.2
Change-Id: Ib553f8c0dacd891e4bd392481ef7b4773386287f