USB: ehci-omap: Get platform resources by index rather than by name

Since there is only one resource per type we don't really need
to use resource name to obtain it. This also also makes it easier
for device tree adaptation.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>