sched/topology,x86: Fix build warning

A compile warning slipped through:

   arch/x86/kernel/smpboot.c:548:5: warning: no previous prototype for function 'arch_sched_node_distance' [-Wmissing-prototypes]

Fixes: 4d6dd05 ("sched/topology: Fix sched domain build error for GNR, CWF in SNC-3 mode")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Author: Peter Zijlstra

arch/x86/include/asm/topology.h

@@ -325,4 +325,6 @@ static inline void freq_invariance_set_perf_ratio(u64 ratio, bool turbo_disabled
 extern void arch_scale_freq_tick(void);
 #define arch_scale_freq_tick arch_scale_freq_tick
 
+extern int arch_sched_node_distance(int from, int to);
+
 #endif /* _ASM_X86_TOPOLOGY_H */