docs: Correct missing "d_" prefix for dentry_operations member d_weak_revalidate

docs: Correct missing "d_" prefix for dentry_operations member d_weak_revalidate

[ Upstream commit af3bc7b313f5674dd725c89c10542064f727a7bd ]

The details for struct dentry_operations member d_weak_revalidate is
missing a "d_" prefix.

Fixes: 1c3f090ad28f ("docs: filesystems: vfs: Convert vfs.txt to RST")
Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20230227184042.2375235-1-development@efficientek.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>