msm: clk: Document clock compatible strings

Pach 5785af3b introduces
checking of compatible strings in .c and .h aswell.

Document clock related compatible strings to avoid
checkpatch warnings.

Change-Id: Ie232ea7d8ea28cb22d5b988011f435bcfbacd4e9
Signed-off-by: Arun KS <arunks@codeaurora.org>