kselftest: ksft_test_num return type should be unsigned

Fixes a compiler warning:

In file included from sync_test.c:37:
../kselftest.h: In function ‘ksft_print_cnts’:
../kselftest.h:78:16: warning: comparison of integer expressions of different signedness: ‘unsigned int’ and ‘int’ [-Wsign-compare]
  if (ksft_plan != ksft_test_num())
                ^~
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/kselftest.h

@@ -36,7 +36,7 @@ struct ksft_count {
 static struct ksft_count ksft_cnt;
 static unsigned int ksft_plan;
 
-static inline int ksft_test_num(void)
+static inline unsigned int ksft_test_num(void)
 {
 	return ksft_cnt.ksft_pass + ksft_cnt.ksft_fail +
 		ksft_cnt.ksft_xfail + ksft_cnt.ksft_xpass +