HID: wacom: generic: Strip off excessive name prefixing

The product name received from the string descriptor in the new MobileStudio
Pro line of tablets begins with "Wacom", which leads to unnecessary visual
noise in the device name when appended to the vendor name which also includes
"Wacom". Look for and fix cases like this.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>