scsi: aacraid: Fix an oops in error handling

If the memdup_user() function fails then it results in an Oops in the
error handling code when we try to kfree() and error pointer.

Link: https://lore.kernel.org/r/20200513093703.GB347693@mwanda
Fixes: 8d925b1f ("scsi: aacraid: Use memdup_user() as a cleanup")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/aacraid/commctrl.c

@@ -516,6 +516,7 @@ static int aac_send_raw_srb(struct aac_dev* dev, void __user * arg)
 	user_srbcmd = memdup_user(user_srb, fibsize);
 	if (IS_ERR(user_srbcmd)) {
 		rcode = PTR_ERR(user_srbcmd);
+		user_srbcmd = NULL;
 		goto cleanup;
 	}