usb: host: ehci-sched: add comment about find_tt() not returning error

Add a comment explaining why find_tt() will not return error even though
find_tt() is checking for NULL and other errors.

Acked-by: Alan Stern <[e-mail]>
Signed-off-by: Sudip Mukherjee <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/host/ehci-sched.c

···
 
 	/* FS/LS bus bandwidth */
 	if (tt_usecs) {
+		/*
+		 * find_tt() will not return any error here as we have
+		 * already called find_tt() before calling this function
+		 * and checked for any error return. The previous call
+		 * would have created the data structure.
+		 */
 		tt = find_tt(qh->ps.udev);
 		if (sign > 0)
 			list_add_tail(&qh->ps.ps_list, &tt->ps_list);
···
 			}
 		}
 
+		/*
+		 * find_tt() will not return any error here as we have
+		 * already called find_tt() before calling this function
+		 * and checked for any error return. The previous call
+		 * would have created the data structure.
+		 */
 		tt = find_tt(stream->ps.udev);
 		if (sign > 0)
 			list_add_tail(&stream->ps.ps_list, &tt->ps_list);