Remove unnecessary NULL assignments

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/library/x509.c b/library/x509.c
index 4035074..812eba8 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -538,14 +538,9 @@
     }
 
 error:
-    prev = NULL;
-
     /* Skip the first element as we did not allocate it */
     allocated = head->next;
 
-    /* Make sure we cannot be followed along this list */
-    head->next = NULL;
-
     while( allocated != NULL )
     {
         prev = allocated;