docs: rbtree.rst: Fix a typo

s/maintanence/maintenance/

Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20210324080046.20709-1-unixbhaskar@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/core-api/rbtree.rst

@@ -201,7 +201,7 @@ search trees, such as for traversals or users relying on a the particular
 order for their own logic. To this end, users can use 'struct rb_root_cached'
 to optimize O(logN) rb_first() calls to a simple pointer fetch avoiding
 potentially expensive tree iterations. This is done at negligible runtime
-overhead for maintanence; albeit larger memory footprint.
+overhead for maintenance; albeit larger memory footprint.
 
 Similar to the rb_root structure, cached rbtrees are initialized to be
 empty via::