drm/stm: ltdc: fix late dereference check

In ltdc_crtc_set_crc_source(), struct drm_crtc was dereferenced in a
container_of() before the pointer check. This could cause a kernel panic.

Fix this smatch warning:
drivers/gpu/drm/stm/ltdc.c:1124 ltdc_crtc_set_crc_source() warn: variable dereferenced before check 'crtc' (see line 1119)

Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/lkml/[e-mail]/
Reported-by: Dan Carpenter <[e-mail]>
Closes: https://lore.kernel.org/lkml/[e-mail]/
Signed-off-by: Raphael Gallais-Pou <[e-mail]>
Acked-by: Philippe Cornu <[e-mail]>
Signed-off-by: Philippe Cornu <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/stm/ltdc.c

···
 
 static int ltdc_crtc_set_crc_source(struct drm_crtc *crtc, const char *source)
 {
-	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
+	struct ltdc_device *ldev;
 	int ret;
 
 	DRM_DEBUG_DRIVER("\n");
 
 	if (!crtc)
 		return -ENODEV;
+
+	ldev = crtc_to_ltdc(crtc);
 
 	if (source && strcmp(source, "auto") == 0) {
 		ldev->crc_active = true;