Update outdated references to the SLRU ControlLock

SLRU bank locks are referred as "bank locks" or "SLRU bank locks" in the
code comments.  The comments updated in this commit use the latter term.

Oversight in 53c2a97a92, that has replaced the single ControlLock by
the bank control locks.

Author: Julien Rouhaud <julien.rouhaud@free.fr>
Discussion: https://postgr.es/m/aLUT2UO8RjJOzZNq@jrouhaud
Backpatch-through: 17

src/backend/access/transam/slru.c

@@ -401,10 +401,10 @@ SimpleLruZeroPage(SlruCtl ctl, int64 pageno)
 	/*
 	 * Assume this page is now the latest active page.
 	 *
-	 * Note that because both this routine and SlruSelectLRUPage run with
-	 * ControlLock held, it is not possible for this to be zeroing a page that
-	 * SlruSelectLRUPage is going to evict simultaneously.  Therefore, there's
-	 * no memory barrier here.
+	 * Note that because both this routine and SlruSelectLRUPage run with a
+	 * SLRU bank lock held, it is not possible for this to be zeroing a page
+	 * that SlruSelectLRUPage is going to evict simultaneously.  Therefore,
+	 * there's no memory barrier here.
 	 */
 	pg_atomic_write_u64(&shared->latest_page_number, pageno);
 

src/include/access/slru.h

@@ -55,7 +55,7 @@ typedef enum
 /*
  * Shared-memory state
  *
- * ControlLock is used to protect access to the other fields, except
+ * SLRU bank locks are used to protect access to the other fields, except
  * latest_page_number, which uses atomics; see comment in slru.c.
  */
 typedef struct SlruSharedData