usb: ehci-platform: use reset array API

Generic drivers like this need to control arbitrary number of reset
lines.  Instead of hard-coding the maximum number of resets, use the
reset array API.  It can manage a bunch of resets behind the scene.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>