ARM: OMAP4: board-4430sdp: don't initialize value that is never used

sdp4430_spi_board_info.irq was initialized to ETH_KS8851_IRQ and in
omap_4430sdp_init() overwritten with gpio_to_irq(ETH_KS8851_IRQ) before
sdp4430_spi_board_info was registered. This is a bit confusing, so
better don't initialize .irq and document that it is set later.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/board-4430sdp.c

@@ -322,7 +322,10 @@ static struct spi_board_info sdp4430_spi_board_info[] __initdata = {
 		.bus_num                = 1,
 		.chip_select            = 0,
 		.max_speed_hz           = 24000000,
-		.irq                    = ETH_KS8851_IRQ,
+		/*
+		 * .irq is set to gpio_to_irq(ETH_KS8851_IRQ)
+		 * in omap_4430sdp_init
+		 */
 	},
 };