docs: path-lookup: Add macro name to symlink limit description

Add macro name MAXSYMLINKS to the symlink limit description, so
that it is consistent with path name length description above.

Signed-off-by: Fox Chen <foxhlchen@gmail.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Link: https://lore.kernel.org/r/20210527091618.287093-7-foxhlchen@gmail.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>