media: exynos4-is: Prevent NULL pointer dereference in __isp_video_try_fmt()

This patch fixes potential NULL pointer dereference as indicated
by the following static checker warning:

drivers/media/platform/exynos4-is/fimc-isp-video.c:408 isp_video_try_fmt_mplane()
error: NULL dereference inside function '__isp_video_try_fmt(isp, &f->fmt.pix_mp, (0))()'.

Fixes: 34947b8a: ("[media] exynos4-is: Add the FIMC-IS ISP capture DMA driver")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/platform/exynos4-is/fimc-isp-video.c

@@ -384,12 +384,17 @@ static void __isp_video_try_fmt(struct fimc_isp *isp,
 				struct v4l2_pix_format_mplane *pixm,
 				const struct fimc_fmt **fmt)
 {
-	*fmt = fimc_isp_find_format(&pixm->pixelformat, NULL, 2);
+	const struct fimc_fmt *__fmt;
+
+	__fmt = fimc_isp_find_format(&pixm->pixelformat, NULL, 2);
+
+	if (fmt)
+		*fmt = __fmt;
 
 	pixm->colorspace = V4L2_COLORSPACE_SRGB;
 	pixm->field = V4L2_FIELD_NONE;
-	pixm->num_planes = (*fmt)->memplanes;
-	pixm->pixelformat = (*fmt)->fourcc;
+	pixm->num_planes = __fmt->memplanes;
+	pixm->pixelformat = __fmt->fourcc;
 	/*
 	 * TODO: double check with the docmentation these width/height
 	 * constraints are correct.