Memtest86+: Fix non-ANSI C function declarations

Change function declarations with an empty parameter list to (void).

Change-Id: Ib1106ed6b52c4038125ff5512f5aef3ccb809e89
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/14177
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-by: Ben Gardner <gardner.ben@gmail.com>
diff --git a/screen_buffer.c b/screen_buffer.c
index a301988..eb7cdc2 100644
--- a/screen_buffer.c
+++ b/screen_buffer.c
@@ -48,7 +48,7 @@
     screen_buf[y][x] = val;
 }
 
-void clear_screen_buf()
+void clear_screen_buf(void)
 {
     int y, x;