[PATCH] HID: elecom: fix the descriptor of the EX-G trackball

ELECOM EX-G has four mouse buttons (one extra plus the normal left,
middle, right buttons), and two extra "back/forward" buttons.

5 out of those 8 buttons are reported in the descriptor. Since the
EX-G HID report is very similar to the DEFT one, this patch reuse
that code to patch the HID report.
---
 drivers/hid/hid-core.c   |  1 +
 drivers/hid/hid-elecom.c | 10 ++++++----
 drivers/hid/hid-ids.h    |  1 +
 3 files changed, 8 insertions(+), 4 deletions(-)