USB: EHCI: return void instead of 0

This patch (as1574) changes the return type of multiple functions in
ehci-sched.c from int to void.  The values they return are now always
0, so there's no reason for them to return any value at all.

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