mtd: ts5500_flash: avoid calling map_destroy on NULL

map_destroy dereferences its argument. The call is furthermore only
reachable when this argument is NULL. Thus the call is dropped.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression *x;
@@

*if (x == NULL)
{ ...
* map_destroy(x);
...
return ...;
}
// </smpl>

Signed-off-by: Julia Lawall <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/maps/ts5500_flash.c

···
 	return 0;
 
 err1:
-	map_destroy(mymtd);
 	iounmap(ts5500_map.virt);
 err2:
 	return rc;