devkit8000: protect board_mmc_init

This function is also defined in omap-common/spl_mmc.de so the implementation
in devkit8000.c was protected by a ifdef.

Signed-off-by: Simon Schwarz <simonschwarzcor@gmail.com>
diff --git a/board/timll/devkit8000/devkit8000.c b/board/timll/devkit8000/devkit8000.c
index f50d113..fee0dff 100644
--- a/board/timll/devkit8000/devkit8000.c
+++ b/board/timll/devkit8000/devkit8000.c
@@ -120,7 +120,7 @@
 	MUX_DEVKIT8000();
 }
 
-#ifdef CONFIG_GENERIC_MMC
+#if defined(CONFIG_GENERIC_MMC) && !defined(CONFIG_SPL_BUILD)
 int board_mmc_init(bd_t *bis)
 {
 	omap_mmc_init(0);