net: sched: pie: fix commenting

Fix punctuation and logical mistakes in the comments. The
logical mistake was that "dequeue_rate" is no longer the default
way to calculate queuing delay and is not needed. The default
way to calculate queue delay was changed in commit cec2975f
("net: sched: pie: enable timestamp based delay calculation").

Signed-off-by: Mohit P. Tahiliani <tahiliani@nitk.edu.in>
Signed-off-by: Leslie Monis <lesliemonis@gmail.com>
Signed-off-by: Gautam Ramakrishnan <gautamramk@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>