ARM: 7153/1: mach-bcmring: fix build error in core.c

Fixes this build error:

CC      arch/arm/mach-bcmring/core.o
arch/arm/mach-bcmring/core.c: In function 'bcmring_init_timer':
arch/arm/mach-bcmring/core.c:238: error: implicit declaration of function 'sp804_clockevents_register'
make[1]: *** [arch/arm/mach-bcmring/core.o] Error 1
make: *** [arch/arm/mach-bcmring] Error 2

Signed-off-by: Maxin B. John <maxin.john@gmail.com>
Reviewed-by: Jiandong Zheng <jdzheng@broadcom.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>