ASoC: audio-ext-clk: update header file name

Update the header file name from audio-ext-clk.h to the
new name qcom,audio-ext-clk.h. The name has been updated
to reflect the upstream style of naming files in dt-binding.

Change-Id: Ib1fb821e5096eaf8779cea002faf3b0b8ed74b58
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>