usb: musb: ux500: harden checks for platform data

In its current state, the ux500-musb driver uses platform data pointers
blindly with no prior checking. If no platform data pointer is passed
this will Oops the kernel. In this patch we ensure platform data and
board data are present prior to using them.

Cc: [e-mail]
Acked-by: Felipe Balbi <[e-mail]>
Acked-by: Fabio Baltieri <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/usb/musb/ux500_dma.c

···
 	struct musb *musb = controller->private_data;
 	struct device *dev = musb->controller;
 	struct musb_hdrc_platform_data *plat = dev->platform_data;
-	struct ux500_musb_board_data *data = plat->board_data;
+	struct ux500_musb_board_data *data;
 	struct dma_channel *dma_channel = NULL;
 	u32 ch_num;
 	u8 dir;
···
 	struct ux500_dma_channel *channel_array;
 	dma_cap_mask_t mask;
 
+	if (!plat) {
+		dev_err(musb->controller, "No platform data\n");
+		return -EINVAL;
+	}
 
+	data = plat->board_data;
 
 	dma_cap_zero(mask);
 	dma_cap_set(DMA_SLAVE, mask);
 
 	/* Prepare the loop for RX channels */
 	channel_array = controller->rx_channel;
-	param_array = data->dma_rx_param_array;
+	param_array = data ? data->dma_rx_param_array : NULL;
 
 	for (dir = 0; dir < 2; dir++) {
 		for (ch_num = 0;
···
 
 		/* Prepare the loop for TX channels */
 		channel_array = controller->tx_channel;
-		param_array = data->dma_tx_param_array;
+		param_array = data ? data->dma_tx_param_array : NULL;
 		is_tx = 1;
 	}