The following checkpatch errors are removed:
ERROR: Bad function definition - void test_btf_add() should probably be 
void test_btf_add(void)
ERROR: Bad function definition - void test_btf_add_btf() should probably 
be void test_btf_add_btf(void)
ERROR: Bad function definition - void test_btf_write() should probably 
be void test_btf_write(void)

Signed-off-by: Jie Shi <shijie001@208suo.com>
---
  tools/testing/selftests/bpf/prog_tests/btf_write.c | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_write.c 
b/tools/testing/selftests/bpf/prog_tests/btf_write.c
index 6e36de1302fc..209a230ffeec 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf_write.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf_write.c
@@ -352,7 +352,7 @@ static void gen_btf(struct btf *btf)
               "\t'v1' val=18446744073709551615", "raw_dump");
  }

-static void test_btf_add()
+static void test_btf_add(void)
  {
      struct btf *btf;

@@ -401,7 +401,7 @@ static void test_btf_add()
      btf__free(btf);
  }

-static void test_btf_add_btf()
+static void test_btf_add_btf(void)
  {
      struct btf *btf1 = NULL, *btf2 = NULL;
      int id;
@@ -497,7 +497,7 @@ static void test_btf_add_btf()
      btf__free(btf2);
  }

-void test_btf_write()
+void test_btf_write(void)
  {
      if (test__start_subtest("btf_add"))
          test_btf_add();