Fix some compile issues for MAI board.

Signed-off-by: Jason Jin <Jason.jin@freescale.com>
diff --git a/board/MAI/AmigaOneG3SE/video.c b/board/MAI/AmigaOneG3SE/video.c
index f6327f7..fc27c68 100644
--- a/board/MAI/AmigaOneG3SE/video.c
+++ b/board/MAI/AmigaOneG3SE/video.c
@@ -56,6 +56,7 @@
 int  video_cols(void);
 
 char *prompt_string = "=>";
+unsigned char video_get_attr(void);
 
 void video_set_color(unsigned char attr)
 {