HID: elecom: extend to fix the descriptor for DEFT trackballs

The ELECOM DEFT trackballs report only five buttons, when the device
actually has 8. Change the descriptor so that the HID driver can see all of
them.

For completeness and future reference, I included a side-by-side diff of
the part of the descriptor that is being edited.

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: Yuxuan Shui <yshuiv7@gmail.com>
Signed-off-by: Diego Elio Pettenò <flameeyes@flameeyes.eu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>