dma-mapping: fix handling of dma-ranges for reserved memory (again)

Daniele reported that issue previously fixed in c41f9ea9
("drivers: dma-coherent: Account dma_pfn_offset when used with device
tree") reappear shortly after 43fc509c ("dma-coherent: introduce
interface for default DMA pool") where fix was accidentally dropped.

Lets put fix back in place and respect dma-ranges for reserved memory.

Fixes: 43fc509c

 ("dma-coherent: introduce interface for default DMA pool")

Reported-by: Daniele Alessandrelli <daniele.alessandrelli@gmail.com>
Tested-by: Daniele Alessandrelli <daniele.alessandrelli@gmail.com>
Tested-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>