selftests: hid: ensure the program is correctly pinned

Turns out that if bpffs was not mounted, the test was silently passing.

So ensure it passes by checking the mount command result.
Signed-off-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

tools/testing/selftests/hid/hid_bpf.c

@@ -640,7 +640,8 @@ TEST_F(hid_bpf, test_attach_detach)
 
 	/* pin the first program and immediately unpin it */
 #define PIN_PATH "/sys/fs/bpf/hid_first_event"
-	bpf_program__pin(self->skel->progs.hid_first_event, PIN_PATH);
+	err = bpf_program__pin(self->skel->progs.hid_first_event, PIN_PATH);
+	ASSERT_OK(err) TH_LOG("error while calling bpf_program__pin");
 	remove(PIN_PATH);
 #undef PIN_PATH
 	usleep(100000);