clk: meson: ao-clkc: claim clock controller input clocks from DT

Instead of relying on a fixed names for the differents input clocks
of the controller, get them through DT.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lkml.kernel.org/r/20190116175435.4990-4-jbrunet@baylibre.com