[ARM] More sparse fixes

arch/arm/kernel/irq.c:998:26: warning: Using plain integer as NULL pointer
arch/arm/kernel/smp.c:145:25: warning: Using plain integer as NULL pointer
arch/arm/kernel/smp.c:362:5: warning: symbol 'smp_call_function_on_cpu' was not declared. Should it be static?
drivers/video/amba-clcd.c:521:12: warning: symbol 'amba_clcdfb_init' was not declared. Should it be static?

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>