clk: nxp: Use new macro CLK_OF_DECLARE_DRIVER

This driver initializes a clock provider via lpc18xx_creg_clk_init
and then continues the initialization on lpc18xx_creg_clk_probe.

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

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
[sboyd@codeaurora.org: s/npx/nxp/ in subject]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>