arm64/spinlock: fix a -Wunused-function warning

mainline inclusion
from mainline-v5.8-rc5
commit 345d52c184dc7de98cff63f1bfa6f90e9db19809
category: bugfix
bugzilla: NA
CVE: NA

--------------------------------

The commit f5bfdc8e3947 ("locking/osq: Use optimized spinning loop for
arm64") introduced a warning from Clang because vcpu_is_preempted() is
compiled away,

kernel/locking/osq_lock.c:25:19: warning: unused function 'node_cpu'
[-Wunused-function]
static inline int node_cpu(struct optimistic_spin_node *node)
                  ^
1 warning generated.

Fix it by converting vcpu_is_preempted() to a static inline function.

Fixes: f5bfdc8e3947 ("locking/osq: Use optimized spinning loop for arm64")
Signed-off-by: NQian Cai <cai@lca.pw>
Acked-by: NWaiman Long <longman@redhat.com>
Reviewed-by: Nzhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

arch/arm64/include/asm/spinlock.h

@@ -29,6 +29,10 @@
  * See:
  * https://lore.kernel.org/lkml/20200110100612.GC2827@hirez.programming.kicks-ass.net
  */
-#define vcpu_is_preempted(cpu)	false
+#define vcpu_is_preempted vcpu_is_preempted
+static inline bool vcpu_is_preempted(int cpu)
+{
+	return false;
+}
 
 #endif /* __ASM_SPINLOCK_H */