Various libata documentation updates.

This is a merger of libata docs + cleanups from
Martin Waitz <tali@admingilde.org> and me.

From: Randy Dunlap <rdunlap@xenotime.net>
From: Martin Waitz <tali@admingilde.org>

Fix libata kernel-doc comments to match code.
Add some function parameters to kernel-doc.
Fix some typos/spellos.
Put comments in <= 80 columns.
Make one DPRINTK string unique.
Fix sparse cast warnings.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>