drivers/video/cg3.c: fix error return code

Convert a nonnegative error return code to a negative one, as returned
elsewhere in the function.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
(
if@p1 (\(ret < 0\|ret != 0\))
 { ... return ret; }
|
ret@p1 = 0
)
... when != ret = e1
    when != &ret
*if(...)
{
  ... when != ret = e2
      when forall
 return ret;
}
// </smpl>
Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>

drivers/video/cg3.c

@@ -398,7 +398,8 @@ static int __devinit cg3_probe(struct platform_device *op)
 			goto out_unmap_screen;
 	}
 
-	if (fb_alloc_cmap(&info->cmap, 256, 0))
+	err = fb_alloc_cmap(&info->cmap, 256, 0);
+	if (err)
 		goto out_unmap_screen;
 
 	fb_set_cmap(&info->cmap, info);