ahci: st: Standardise naming conventions

Other devices have adopted similar naming conventions which have been
accepted as the standard. This patch brings any mention of the the ST
AHCI driver into line with them.

Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Tejun Heo <tj@kernel.org>