ata: ahci: Fix usage on big-endian platforms

This patch adds a few missing virt_to_phys() to use the correct physical
address for DMA operations in the common AHCI code. This is done to
support the big-endian MIPS Octeon platform.

Additionally the code a cleaned up a bit (remove some empty lines) and
made a bit better readable.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Aaron Williams <awilliams@marvell.com>
Cc: Chandrakala Chavva <cchavva@marvell.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>