mhi: core: rename iova address to dma_addr

dma_addr are not necessarily same as physical address if iova is
enabled, rename to correct name to avoid confusions.

CRs-Fixed: 2258358
Change-Id: If55418500f94fcc9ebdc08786adea8bbf398cad3
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>