staging: line6: Changed strict_strtoul() to kstrtou8() in pod_set_midi_postprocess()

Changed a call to strict_strtoul() into kstrtou8() in
pod_set_midi_postprocess().

Signed-off-by: Johannes Thumshirn <morbidrsa@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>