board: colibri_vf: fix compiling warning

This patch fixes the following compiler warning:
=============
board/toradex/colibri_vf/colibri_vf.c: In function 'ft_board_setup':
board/toradex/colibri_vf/colibri_vf.c:436:6: warning: unused variable 'ret' [-Wunused-variable]
=============

Fixes: be3f1a56 ("video: fsl_dcu_fb: add DM_VIDEO support")
Signed-off-by: NOleksandr Suvorov <oleksandr.suvorov@toradex.com>

board/toradex/colibri_vf/colibri_vf.c

@@ -433,7 +433,7 @@ int checkboard(void)
 #if defined(CONFIG_OF_LIBFDT) && defined(CONFIG_OF_BOARD_SETUP)
 int ft_board_setup(void *blob, struct bd_info *bd)
 {
-#ifndef CONFIG_DM_VIDEO
+#if defined(CONFIG_VIDEO_FSL_DCU_FB) && !defined(CONFIG_DM_VIDEO)
 	int ret = 0;
 #endif
 #ifdef CONFIG_FDT_FIXUP_PARTITIONS