[PATCH][SRU][Xenial] The Precision Touchpad(PTP) button sends incorrect event code

[AceLan Kao]

BugLink: https://bugs.launchpad.net/bugs/1708372

[Impact]
The touchpad right button should send 273(BTN_RIGHT),
and the left button should send 272(BTN_LEFT)
But the touchpad right button sends 274(BTN_MIDDLE),
and the left button sends 273 (BTN_RIGHT)

[Fix]
The fix is pretty simple to just decrease the event code by 1.

[Test Case]
Verified on the machine has this issue, and confirm this patch works.

[Regression Potential]
The patch has strict if statement, so it won't affect other touchpad devices.
And no more rework on this code snip after this commit.

Benjamin Tissoires (1):
  HID: multitouch: handle external buttons for Precision Touchpads

 drivers/hid/hid-multitouch.c | 8 ++++++++
 1 file changed, 8 insertions(+)

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2.7.4