[media] drivers/media/video/atmel-isi.c: eliminate a null pointer dereference

[media] drivers/media/video/atmel-isi.c: eliminate a null pointer dereference

The variable isi might be null or might be freed at the point of the call
to clk_put.  pclk contains the value that isi->pclk is expected to point to.

The semantic match that finds this problem is as follows:

// <smpl>
@r@
expression E, E1;
identifier f;
statement S1,S2,S3;
@@

if (E == NULL)
{
  ... when != if (E == NULL || ...) S1 else S2
      when != E = E1
*E->f
  ... when any
  return ...;
}
else S3
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>