MAINTAINERS: clk: discuss on the linux-clk@vger.kernel.org list

Most Linux clock framework discussions take place on the
linux-kernel@vger.kernel.org or linux-arm-kernel@lists.infradead.org
mailing lists.  The volume of unrelated messages on these lists makes
it difficult for non-maintainers to follow along with discussions.
Switch the discussion list for clock framework discussions to
linux-clk@vger.kernel.org.  Also, add linux-clk@vger.kernel.org as a
mailing list for clock API discussions.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
Cc: Tomasz Figa <tomasz.figa@gmail.com>
Cc: Viresh Kumar <viresh.linux@gmail.com>
Cc: Peter De Schrijver <pdeschrijver@nvidia.com>
Cc: Prashant Gaikwad <pgaikwad@nvidia.com>
Cc: Tero Kristo <t-kristo@ti.com>
Cc: Russell King <linux@arm.linux.org.uk>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Michael Turquette <mturquette@linaro.org>