kcov: make some symbols static

Fix sparse build warnings:

kernel/kcov.c:99:1: warning:
 symbol '__pcpu_scope_kcov_percpu_data' was not declared. Should it be static?
kernel/kcov.c:778:6: warning:
 symbol 'kcov_remote_softirq_start' was not declared. Should it be static?
kernel/kcov.c:795:6: warning:
 symbol 'kcov_remote_softirq_stop' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Link: http://lkml.kernel.org/r/20200702115501.73077-1-weiyongjun1@huawei.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kcov.c

@@ -96,7 +96,7 @@ struct kcov_percpu_data {
 	int			saved_sequence;
 };
 
-DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data);
+static DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data);
 
 /* Must be called with kcov_remote_lock locked. */
 static struct kcov_remote *kcov_remote_find(u64 handle)
@@ -775,7 +775,7 @@ static inline bool kcov_mode_enabled(unsigned int mode)
 	return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED;
 }
 
-void kcov_remote_softirq_start(struct task_struct *t)
+static void kcov_remote_softirq_start(struct task_struct *t)
 {
 	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
 	unsigned int mode;
@@ -792,7 +792,7 @@ void kcov_remote_softirq_start(struct task_struct *t)
 	}
 }
 
-void kcov_remote_softirq_stop(struct task_struct *t)
+static void kcov_remote_softirq_stop(struct task_struct *t)
 {
 	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);