mhi_dev: mhi: avoid unnecessary memory calls

Avoid calling dma_map_single and dma_unmap_single
for the memory that is allocated using
dma_alloc_coherent as we already have the physical
address available.

Change-Id: I80fb55a9d76ae8dee2513496ff55d1ab49fb27f7
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>
Signed-off-by: Chandra Devireddy <cdevired@codeaurora.org>