HID: fix incorrect handling of devices with high button count

Button names for USB gamepads are currently assigned incorrectly, as the evdev
code assigned to buttons is "BTN_GAMEPAD + code", which on devices with more
then 16 buttons bleeds over into button names reserved for graphic tablets
(BTN_TOOL_PEN, etc.). This causes problems further down the line as the device
are now no longer detected as joystick. This patch fixes that by assigning
buttons outside the range to BTN_TRIGGER_HAPPY (as is already the case for USB
joysticks).

Furthermore this patch corrects the assignment to BTN_TRIGGER_HAPPY, as
currently the first button over 16 is assigned to BTN_TRIGGER_HAPPY17 (i.e.
BTN_TRIGGER_HAPPY+0x10) not BTN_TRIGGER_HAPPY.

Signed-off-by: Ingo Ruhnke <grumbel@gmail.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>