clk: mmp: avoid missing prototype warning

The kernel test robot points out two harmless warnings in the
mmp clk drivers:

drivers/clk/mmp/clk-pxa168.c:68:13: warning: no previous prototype for 'pxa168_clk_init' [-Wmissing-prototypes]
drivers/clk/mmp/clk-pxa910.c:66:13: warning: no previous prototype for 'pxa910_clk_init' [-Wmissing-prototypes]

Fix these by including corresponding header file.

Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Stephen Boyd <[e-mail]>

drivers/clk/mmp/clk-pxa168.c

···
  */
 
 #include <linux/clk.h>
+#include <linux/clk/mmp.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/spinlock.h>

drivers/clk/mmp/clk-pxa910.c

···
  */
 
 #include <linux/clk.h>
+#include <linux/clk/mmp.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/spinlock.h>