mfd: menelaus: Use NULL instead of 0

'mmc_callback_data' and 'vtg' are pointers.

Fix the following sparse warning:

drivers/mfd/menelaus.c:445:43: warning: Using plain integer as NULL pointer
drivers/mfd/menelaus.c:469:20: warning: Using plain integer as NULL pointer
Signed-off-by: NJingoo Han <jg1.han@samsung.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

drivers/mfd/menelaus.c

@@ -442,7 +442,7 @@ void menelaus_unregister_mmc_callback(void)
 	menelaus_remove_irq_work(MENELAUS_MMC_S2D1_IRQ);
 
 	the_menelaus->mmc_callback = NULL;
-	the_menelaus->mmc_callback_data = 0;
+	the_menelaus->mmc_callback_data = NULL;
 }
 EXPORT_SYMBOL(menelaus_unregister_mmc_callback);
 
@@ -466,7 +466,7 @@ static int menelaus_set_voltage(const struct menelaus_vtg *vtg, int mV,
 	struct i2c_client *c = the_menelaus->client;
 
 	mutex_lock(&the_menelaus->lock);
-	if (vtg == 0)
+	if (!vtg)
 		goto set_voltage;
 
 	ret = menelaus_read_reg(vtg->vtg_reg);