HID: wacom: Fix ABS_MISC reporting for Cintiq Companion 2

The pad handling code introduced for the Cintiq Companion 2 (f7acb55c)
looks at the wrong bytes in the report when deciding whether ABS_MISC
should be sent. This does not cause any issues with the X driver now
that the pen and pad have been split to separate devices, but is
incorrect and has caused issues when backporting to distros with pre-
3.17 kernels.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>