MAINTAINERS: make drivers/clk entry match subdirs

Modify the drivers/clk MAINTAINERS entry so that it matches the entire
drivers/clk tree, with the exception of clkdev.c which has a separate
entry. Make a similar change to pick up all clk-related header files.

This causes get_maintainers.pl to spit out the expected results for any
patches to clock drivers that are in sub-directories of drivers/clk,
e.g. drivers/clk/tegra/.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>