Don't use cl_git_pass for POSIX functions

If there is a failure then cl_git_pass tries to get the libgit2
error, but p_... functions don't set that.

Also - trailing whitespace cleanup.

tests/describe/describe_helpers.c

@@ -16,7 +16,7 @@ void assert_describe(
 	cl_git_pass(git_describe_commit(&result, object, opts));
 	cl_git_pass(git_describe_format(&label, result, fmt_opts));
 
-	cl_git_pass(p_fnmatch(expected_output, git_buf_cstr(&label), 0));
+	cl_must_pass(p_fnmatch(expected_output, git_buf_cstr(&label), 0));
 
 	git_describe_result_free(result);
 	git_object_free(object);
@@ -35,7 +35,7 @@ void assert_describe_workdir(
 	cl_git_pass(git_describe_workdir(&result, repo, opts));
 	cl_git_pass(git_describe_format(&label, result, fmt_opts));
 
-	cl_git_pass(p_fnmatch(expected_output, git_buf_cstr(&label), 0));
+	cl_must_pass(p_fnmatch(expected_output, git_buf_cstr(&label), 0));
 
 	git_describe_result_free(result);
 	git_buf_free(&label);