usb: host: remove unnecessary null check

Remove unnecessary null check. udev->tt cannot ever be NULL when this
section of code runs.

Addresses-Coverity-ID: 100828
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-sched.c

@@ -1105,7 +1105,7 @@ iso_stream_init(
 		addr |= epnum << 8;
 		addr |= dev->devnum;
 		stream->ps.usecs = HS_USECS_ISO(maxp);
-		think_time = dev->tt ? dev->tt->think_time : 0;
+		think_time = dev->tt->think_time;
 		stream->ps.tt_usecs = NS_TO_US(think_time + usb_calc_bus_time(
 				dev->speed, is_input, 1, maxp));
 		hs_transfers = max(1u, (maxp + 187) / 188);