Documentation/admin-guide: tainted-kernels: Fix typo occured

Fix typo.
s/occured/occurred/

Signed-off-by: Naoki Hayama <naoki.hayama@lineo.co.jp>
Link: https://lore.kernel.org/r/20201012082441.5831-1-naoki.hayama@lineo.co.jp
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Author: Naoki Hayama

Documentation/admin-guide/tainted-kernels.rst

@@ -130,7 +130,7 @@ More detailed explanation for tainting
  5)  ``B`` If a page-release function has found a bad page reference or some
      unexpected page flags. This indicates a hardware problem or a kernel bug;
      there should be other information in the log indicating why this tainting
-     occured.
+     occurred.
 
  6)  ``U`` if a user or user application specifically requested that the
      Tainted flag be set, ``' '`` otherwise.