Fix grammar in virtual input device driver section

Change "The drivers needs" to "The driver needs" to correct a
subject-verb disagreement and improve readability.

lkmpg.tex

@@ -2055,7 +2055,7 @@ After that, registers it by calling \cpp|input_register_device()|.
 
 Here is an example, vinput,
 It is an API to allow easy development of virtual input drivers.
-The drivers needs to export a \cpp|vinput_device()| that contains the virtual device name and \cpp|vinput_ops| structure that describes:
+The driver needs to export a \cpp|vinput_device()| that contains the virtual device name and \cpp|vinput_ops| structure that describes:
 
 \begin{itemize}
     \item the init function: \cpp|init()|