IB/core: Remove ib_sg_dma_address() and ib_sg_dma_len()

Keeping single line wrapper functions is not useful. Hence remove the
ib_sg_dma_address() and ib_sg_dma_len() functions. This patch does not
change any functionality.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>