staging: line6: avoid CamelCase POD_* enums in pod.c

Fix the following checkpatch.pl warnings:

  WARNING: Avoid CamelCase: <POD_monitor_level>
  #4512: FILE: staging/line6/pod.c:41:
  +       POD_monitor_level  = 0x04,

  WARNING: Avoid CamelCase: <POD_system_invalid>
  #4513: FILE: staging/line6/pod.c:42:
  +       POD_system_invalid = 0x10000

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>