drivers/dma: Correct NULL test

cohd_fin has already been verified not to be NULL, so the argument to
BUG_ON cannot be true.

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

// <smpl>
@r@
expression *x;
expression e;
identifier l;
@@

if (x == NULL || ...) {
    ... when forall
    return ...; }
... when != goto l;
    when != x = e
    when != &x
*x == NULL
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/coh901318.c

@@ -613,8 +613,6 @@ static void dma_tasklet(unsigned long data)
 	cohd_fin->pending_irqs--;
 	cohc->completed = cohd_fin->desc.cookie;
 
-	BUG_ON(cohc->nbr_active_done && cohd_fin == NULL);
-
 	if (cohc->nbr_active_done == 0)
 		return;