arm: atmel: at91sam9x5: cleanup cs configure for spi

As the cs for spi is worked in gpio mode, so no need to configure
it as peripheral and then configure to gpio. Configure it to gpio
directly.
Signed-off-by: NBo Shen <voice.shen@atmel.com>
Signed-off-by: NAndreas Bießmann <andreas.devel@googlemail.com>

board/atmel/at91sam9x5ek/at91sam9x5ek.c

@@ -271,7 +271,6 @@ int board_init(void)
 #endif
 
 #ifdef CONFIG_ATMEL_SPI
-	at91_spi0_hw_init(1 << 0);
 	at91_spi0_hw_init(1 << 4);
 #endif