i3c: mipi-i3c-hci: Do not unmap region not mapped for transfer

Fix following warning (with CONFIG_DMA_API_DEBUG) which happens with a
transfer without a data buffer.

	DMA-API: i3c mipi-i3c-hci.0: device driver tries to free DMA memory it has not allocated [device address=0x0000000000000000] [size=0 bytes]

For those transfers the hci_dma_queue_xfer() doesn't create a mapping and
the DMA address pointer xfer->data_dma is not set.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Link: https://lore.kernel.org/r/20230921055704.1087277-10-jarkko.nikula@linux.intel.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>