firewire: ohci: use devres for MMIO region mapping

The PCI framework has the convenient helper function to check and map MMIO
region with managed device resource.

This commit elaborates 1394 OHCI driver to use the function.

Link: https://lore.kernel.org/r/20230604054451.161076-4-o-takashi@sakamocchi.jp


Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>