Staging: dst: correct error-handling code

dst_state_alloc returns an ERR_PTR value in an error case instead of NULL.

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

// <smpl>
@match exists@
expression x, E;
statement S1, S2;
@@

x = dst_state_alloc(...)
... when != x = E
(
* if (x == NULL || ...) S1 else S2
|
* if (x == NULL && ...) S1 else S2
)
// </smpl>

Signed-off-by: Julia Lawall <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/dst/export.c

···
 		goto err_out_exit;
 
 	new = dst_state_alloc(st->node);
-	if (!new) {
+	if (IS_ERR(new)) {
 		err = -ENOMEM;
 		goto err_out_release;
 	}