Documentation: fix filesystems/locking.rst malformed table warnings

Documentation: fix filesystems/locking.rst malformed table warnings

Fix Sphinx malformed table warnings in filesystems/locking.rst:

lnx-58-rc1/Documentation/filesystems/locking.rst:443: WARNING: Malformed table.
Text in column margin in table line 8.

lnx-58-rc1/Documentation/filesystems/locking.rst:620: WARNING: Malformed table.
Text in column margin in table line 2.

Fixes: ec23eb54fbc7 ("docs: fs: convert docs without extension to ReST")
Fixes: c1e8d7c6a7a6 ("mmap locking API: convert mmap_sem comments")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Michel Lespinasse <walken@google.com>
Link: https://lore.kernel.org/r/12c2afd1-2dcf-2ea0-02aa-bc2759729c77@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>