HID: core: for input reports, process the usages by priority list

Now that we have a list of fields/usages by priority order,
walk through that list to process the inputs instead of using the
order provided by the manufacturer.

Note that this changes the way we update the values in the struct
hid_field:
Previously, once a field was processed, we updated the new values.
Now we need to wait for the entire report to be processed to update
the values.

I don't think it will be an issue: because we were relying on the device
ordering, there were no guarantees to have a field stored before an other.
Which is why we introduced .report() in drivers to have those values
updated.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>