[media] drivers/media/pci/cx25821/cx25821-video-upstream-ch2.c: fix error return...

[media] drivers/media/pci/cx25821/cx25821-video-upstream-ch2.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>

While here, replace strlen()+kmemdup() to kstrdup().

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Reviewed-by: walter harms <wharms@bfs.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>