xfrm: Remove unnecessary NULL check in xfrm_lookup_with_ifid()

This NULL check is unnecessary and can be removed.  It confuses
Smatch static analysis tool because it makes Smatch think that
xfrm_lookup_with_ifid() can return a mix of NULL pointers and errors so
it creates a lot of false positives.  Remove it.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_policy.c

@@ -3294,7 +3294,7 @@ struct dst_entry *xfrm_lookup_with_ifid(struct net *net,
 
 ok:
 	xfrm_pols_put(pols, drop_pols);
-	if (dst && dst->xfrm &&
+	if (dst->xfrm &&
 	    (dst->xfrm->props.mode == XFRM_MODE_TUNNEL ||
 	     dst->xfrm->props.mode == XFRM_MODE_IPTFS))
 		dst->flags |= DST_XFRM_TUNNEL;