pie: fix kernel-doc notation warning

Spell a struct member's name correctly to prevent a kernel-doc
warning.

pie.h:38: warning: Function parameter or member 'tupdate' not described in 'pie_params'

Fixes: b42a3d7c ("pie: improve comments and commenting style")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Leslie Monis <lesliemonis@gmail.com>
Cc: "Mohit P. Tahiliani" <tahiliani@nitk.edu.in>
Cc: Gautam Ramakrishnan <gautamramk@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Link: https://lore.kernel.org/r/20230714045127.18752-9-rdunlap@infradead.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>