[BUGFIX] t3lib_userAuthGroup::checkLogFailures() gives PHP notice

Due to improper method signature in the parent class of t3lib_userAuthGroup,
a PHP notice is generated when calling method checkLogFailures().

Change-Id: Ic41cb88889ee18f2508ae5b2e96858e8bf16c349
Fixes: #30055
Releases: 4.6
Reviewed-on: http://review.typo3.org/5082
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers