MIPS: cevt-ds1287: Add missing ds1287.h include

MIPS: cevt-ds1287: Add missing ds1287.h include

Address the issue of cevt-ds1287.c not including the ds1287.h header
file.

Fix follow errors with gcc-14 when -Werror:

arch/mips/kernel/cevt-ds1287.c:15:5: error: no previous prototype for ‘ds1287_timer_state’ [-Werror=missing-prototypes]
   15 | int ds1287_timer_state(void)
      |     ^~~~~~~~~~~~~~~~~~
arch/mips/kernel/cevt-ds1287.c:20:5: error: no previous prototype for ‘ds1287_set_base_clock’ [-Werror=missing-prototypes]
   20 | int ds1287_set_base_clock(unsigned int hz)
      |     ^~~~~~~~~~~~~~~~~~~~~
arch/mips/kernel/cevt-ds1287.c:103:12: error: no previous prototype for ‘ds1287_clockevent_init’ [-Werror=missing-prototypes]
  103 | int __init ds1287_clockevent_init(int irq)
      |            ^~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[7]: *** [scripts/Makefile.build:207: arch/mips/kernel/cevt-ds1287.o] Error 1
make[7]: *** Waiting for unfinished jobs....
make[6]: *** [scripts/Makefile.build:465: arch/mips/kernel] Error 2
make[6]: *** Waiting for unfinished jobs....

Signed-off-by: WangYuli <wangyuli@uniontech.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>