clk: axis: Use new macro CLK_OF_DECLARE_DRIVER

This driver initializes a clock provider via of_artpec6_clkctrl_setup
and then continues the initialization on artpec6_clkctrl_probe.

Use the new macro to notify the clk subsystem about this behaviour.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>