USB: ehci-omap: Use devm_ioremap_resource()

Make use of devm_ioremap_resource() and correct comment.

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>