Update bottomhalf description to use workqueue

Since commit 3682d9e switched the implementation to workqueues,
update the description accordingly to avoid confusion.

Author: eleanorLYJ

lkmpg.tex

@@ -1985,7 +1985,8 @@ \subsection{Detecting button presses}
 \subsection{Bottom Half}
 \label{sec:bottom_half}
 Suppose you want to do a bunch of stuff inside of an interrupt routine.
-A common way to do that without rendering the interrupt unavailable for a significant duration is to combine it with a tasklet.
+A common way to avoid blocking the interrupt for a significant duration
+is to defer the time-consuming part to a workqueue.
 This pushes the bulk of the work off into the scheduler.
 
 The example below modifies the previous example to also run an additional task when an interrupt is triggered.