clk: mxs: fix clock lookup after freeing init memory

The struct clk_lookup are marked as __initdata, resulting in being
removed from memory after the kernel finished booting. However this
leads to a NULL pointer de-ref if loading a module which uses clk_get.

This patch removes the __initdata from the struct clk_lookup.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>