USB: storage: unusual_devs entry for Mio C520-GPS

This patch (as1176) adds an unusual_devs entry for the Mio C520 GPS
unit.  Other devices also based on the Mitac hardware use the same USB
interface firmware, so the Vendor and Product names are generalized.

This fixes Bugzilla #11583.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Tamas Kerecsen <kerecsen@bigfoot.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>