drivers/video: bad error test before a dereference

The error test that follows the call to backlight_device_register semms
not to concern the right variable.

A simplified version of the semantic match that finds this problem is
as follows:
(http://www.emn.fr/x-info/coccinelle/)
// <smpl>
@def0@
expression x;
position p0;
@@
x@p0 = backlight_device_register(...)

@protected@
expression def0.x,E;
position def0.p0;
position p;
statement S;
@@
x@p0
... when != x = E
if (!IS_ERR(x) && ...) {<... x@p ...>} else S

@unprotected@
expression def0.x;
identifier fld;
position def0.p0;
position p != protected.p;
@@
x@p0
... when != x = E
* x@p->fld
// </smpl>

Signed-off-by: Julien Brunel <brunel@diku.dk>
Signed-off-by: Julia Lawall <julia@diku.dk>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/atmel_lcdfb.c

@@ -132,7 +132,7 @@ static void init_backlight(struct atmel_lcdfb_info *sinfo)
 
 	bl = backlight_device_register("backlight", &sinfo->pdev->dev,
 			sinfo, &atmel_lcdc_bl_ops);
-	if (IS_ERR(sinfo->backlight)) {
+	if (IS_ERR(bl)) {
 		dev_err(&sinfo->pdev->dev, "error %ld on backlight register\n",
 				PTR_ERR(bl));
 		return;