clk: make several parent names const

Since commit 2893c379 ("clk: make strings in parent name arrays
const") the name of parent clocks can be const. So add more const in
several clock drivers.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>