EHCI: local variable for port status register

This patch (as708) introduces a local variable to hold the port
status-register address in ehci-hub.c.  There's not much improvement
in the object code, but it sure is a lot easier to read.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>