ARM: omap2: fix missing tick_broadcast() prototype

omap2 contains a hack to define tick_broadcast() on non-SMP
configurations in place of the normal SMP definition. This one
causes a warning because of a missing prototype:

arch/arm/mach-omap2/board-generic.c:44:6: error: no previous prototype for 'tick_broadcast'

Make sure to always include the header with the declaration.

Fixes: d86ad463 ("ARM: OMAP2+: Fix regression for using local timer on non-SMP SoCs")
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Link: https://lore.kernel.org/r/20230516153109.514251-9-arnd@kernel.orgSigned-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/mach-omap2/board-generic.c

@@ -13,6 +13,7 @@
 #include <linux/of_platform.h>
 #include <linux/irqdomain.h>
 #include <linux/clocksource.h>
+#include <linux/clockchips.h>
 
 #include <asm/setup.h>
 #include <asm/mach/arch.h>