m68k: 68000: fix warning in timer code

When building with W=1:

      CC      arch/m68k/68000/timers.o
    arch/m68k/68000/timers.c:120:5: warning: no previous prototype for ‘m68328_hwclk’ [-Wmissing-prototypes]
     int m68328_hwclk(int set, struct rtc_time *t)
         ^~~~~~~~~~~~

Include m68328.h to get prototype for m68328_hwclk().
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>

arch/m68k/68000/timers.c

@@ -25,6 +25,8 @@
 #include <asm/machdep.h>
 #include <asm/MC68VZ328.h>
 
+#include "m68328.h"
+
 /***************************************************************************/
 
 #if defined(CONFIG_DRAGEN2)