pgsql: Update outdated references to the SLRU ControlLock

Update outdated references to the SLRU ControlLock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 53c2a97a9266, that has replaced the single ControlLock by
the bank control locks.

Author: Julien Rouhaud <julien.rouhaud@free.fr>
Discussion: /messages/by-id/aLUT2UO8RjJOzZNq@jrouhaud
Backpatch-through: 17

Branch
------
REL_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/399f7ce3daa692a5bebbba50bf9cb773f6469613

Modified Files
--------------
src/backend/access/transam/slru.c | 8 ++++----
src/include/access/slru.h | 2 +-
2 files changed, 5 insertions(+), 5 deletions(-)