ARM: at91: fix external interrupt specification in board code

Since the switch to sparse irq, we have to add the NR_IRQS_LEGACY
offset to static irq numbers. It has been forgotten on these
SPI irq definitions in board code.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: stable <stable@vger.kernel.org> [v3.6]