ARM: at91: init CAN clock in at91sam9x5

During the registeration of clocks, the CAN clock wasn't added to the
periph_clocks_lookups table. Add them now.

Signed-off-by: Yoann Di Ruzza <ydiruzza@gmail.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>