MIPS: SGI-IP27: Remove duplicated include in ip27-timer.c

After commit 9d0aaf98 ("MIPS: SGI-IP27: Move all shared IP27
declarations to ip27-common.h"), ip27-common.h is included more
than once in ip27-timer.c, remove it.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>