h8300/time: add missing #include <asm/irq_regs.h>

Fix the build error:

  arch/h8300/kernel/time.c: In function 'h8300_timer_tick':
  arch/h8300/kernel/time.c:39:2: error: implicit declaration of function 'get_irq_regs' [-Werror=implicit-function-declaration]
  arch/h8300/kernel/time.c:39:42: error: invalid type argument of '->' (have 'int')

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>