include: clock: remove ifdef from header file

As audio-ext-clk.h is finally included in device tree and
and using ifdef results in compilation failure. Delete
ifdef from audio-ext-clk.h.

CRs-Fixed: 1090500
Change-Id: Ib6f715c3f606770e7e0b1f0f84ab50e442398cd0
Signed-off-by: Meng Wang <mwang@codeaurora.org>