hid: bump HID_ITEM_MAXUSAGES to 8

My YOGA requires a minimum of 7 to parse w/o an error. Since the memory savings
are trivial and the yoga a popular system, bump the default up to 8. There's no
API/ABI issues in doing this. This hid_item struct isn't exported to userland
and the one libusbhid has is different and only shares a name...

MFC After: 3 days
Reviewed by: wulf@
Differential Revision: https://reviews.freebsd.org/D28543