sata_fsl: remove check for CONFIG_MPC8315_DS

A check for CONFIG_MPC8315_DS was added in v2.6.24. But the related
Kconfig symbol was never added to the tree. So the code behind this
check has effectively been dead for over six years. Remove it.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Tejun Heo <tj@kernel.org>