usb: ohci-at91: replace request_mem_region + ioremap by devm_ioremap_resource

Replace the request_mem_region + ioremap calls by the
devm_ioremap_resource call which does the same things but with device
managed resources.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>