docs: linuxdevices is dead, switch to linuxgizmos

linuxdevices.com has been dead for some time now when it was bought out.
Switch to linuxgizmos.com which is the new page of the author.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>