fix:memory:of_memory:add missing header dependencies

We get 2 warnings when biuld kernel with W=1:
drivers/memory/of_memory.c:30:30: warning: no previous prototype for 'of_get_min_tck' [-Wmissing-prototypes]
drivers/memory/of_memory.c:106:30: warning: no previous prototype for 'of_get_ddr_timings' [-Wmissing-prototypes]

In fact, these functions are declared in drivers/memory/of_memory.h
so this patch add missing header dependencies.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>