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

include/net/pie.h

@@ -17,7 +17,7 @@
 /**
  * struct pie_params - contains pie parameters
  * @target:		target delay in pschedtime
- * @tudpate:		interval at which drop probability is calculated
+ * @tupdate:		interval at which drop probability is calculated
  * @limit:		total number of packets that can be in the queue
  * @alpha:		parameter to control drop probability
  * @beta:		parameter to control drop probability