HID: wacom: Move HID fix for AES serial number into wacom_hid_usage_quirk

The 'wacom_hid_usage_quirk' function is the intended home for fixing
up descriptors that are buggy or that don't quite fit the mold. Commit
57832512 was supposed to move all of these quirks but it missed the
code to handle fixup the serial number usages for AES pens. Lets move
this code out of 'wacom_wac_pen_usage_mapping' where it was previously
lurking and put it into the same place as the others.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>