USB: EHCI: code rearrangement in iso_stream_schedule()

This patch interchanges the "if" and "else" branches of the big "if"
statement in iso_stream_schedule(), in preparation for the next patch
in this series.  That is, it changes

	if (likely(!...)) {
		A
	} else {
		B
	}

to

	if (unlikely(...)) {
		B
	} else {
		A
	}

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>