ataflop: adjust NULL test

dtp is derefenced on the lines above the test !dtp, and so it cannot be
NULL at this point.

A simplified version of the semantic match that finds this problem is as
follows: (http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@r@
expression x,E,E1;
identifier f,l;
position p1,p2;
@@

*x@p1->f = E1;
... when != x = E
    when != goto l;
(
*x@p2 == NULL
|
*x@p2 != NULL
)
// </smpl>
Signed-off-by: NJulia Lawall <julia@diku.dk>
Signed-off-by: NTejun Heo <tj@kernel.org>

drivers/block/ataflop.c

@@ -1627,7 +1627,7 @@ static int fd_ioctl(struct block_device *bdev, fmode_t mode,
 				drive, dtp->blocks, dtp->spt, dtp->stretch);
 
 		/* sanity check */
-		if (!dtp || setprm.track != dtp->blocks/dtp->spt/2 ||
+		if (setprm.track != dtp->blocks/dtp->spt/2 ||
 		    setprm.head != 2) {
 			redo_fd_request();
 			return -EINVAL;