drivers/video/imxfb.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/imxfb.c

@@ -803,6 +803,7 @@ static int __init imxfb_probe(struct platform_device *pdev)
 	fbi->regs = ioremap(res->start, resource_size(res));
 	if (fbi->regs == NULL) {
 		dev_err(&pdev->dev, "Cannot map frame buffer registers\n");
+		ret = -ENOMEM;
 		goto failed_ioremap;
 	}