ARM: at91: fix spi cs on sama5d3 Xplained board

The PD16 is the CS3 for SPI0 while not SPI1.

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>