USB: fix ehci alignment error

The Kirkwood gave an unaligned memory access error on
line 742 of drivers/usb/host/echi-hcd.c:
"ehci->last_periodic_enable = ktime_get_real();"

Signed-off-by: Harro Haan <hrhaan@gmail.com>
Cc: stable <stable@kernel.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>