video: ipuv3_fb: skip IPU shutdown if IPU was not enabled before

Boards can skip display interface init using board_video_skip().
If display interface was not initialized (e.g. no ipuv3 framebuffer
registered or IPU clock disabled), booting Linux stops due to the
crash in IPU shutdown function, when accessing IPU registers.
Check IPU clock and skip shutdown if clock is not enabled.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
diff --git a/drivers/video/mxc_ipuv3_fb.c b/drivers/video/mxc_ipuv3_fb.c
index 0d0a0a9..1ab5cb7 100644
--- a/drivers/video/mxc_ipuv3_fb.c
+++ b/drivers/video/mxc_ipuv3_fb.c
@@ -571,6 +571,9 @@
 	int i;
 	struct ipu_stat *stat = (struct ipu_stat *)IPU_STAT;
 
+	if (!ipu_clk_enabled())
+		return;
+
 	for (i = 0; i < ARRAY_SIZE(mxcfb_info); i++) {
 		struct fb_info *fbi = mxcfb_info[i];
 		if (fbi) {