FSNamesystem.mkdirsInt should call the getAuditFileInfo() wrapper

In FSNamesystem.java, getAuditFileInfo() is the canonical way to get file info for auditing purpose. getAuditFileInfo() returns null when auditing is disabled, and calls dir.getFileInfo() when auditing is enabled.

One internal APIs, mkdirsInt() mistakenly use the raw dir.getFileInfo() to get file info for auditing. Should change to getAuditFileInfo().

Note that another internal API, startFileInt() uses dir.getFileInfo() correctly, because the returned file stat is returned out.