clk: Remove comment for end of CONFIG_COMMON_CLK section

The comment is inaccurate (it actually ends the CONFIG_COMMON_CLK
section, there's no else) and given that we've just got a single level
of ifdef isn't really needed anyway.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>