USB: make actual_length in struct urb field u32

actual_length should also be a u32 and not a signed value.  This patch
changes this field to be 'u32' to prevent any potential negative
conversion and comparison errors.

This triggered a few compiler warning messages when these fields were
being used with the min macro, so they have also been fixed up in this
patch.

Cc: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/ftdi_sio.c

@@ -1947,7 +1947,7 @@ static void ftdi_process_read(struct work_struct *work)
 			priv->prev_status = new_status;
 		}
 
-		length = min(PKTSZ, urb->actual_length-packet_offset)-2;
+		length = min_t(u32, PKTSZ, urb->actual_length-packet_offset)-2;
 		if (length < 0) {
 			dev_err(&port->dev, "%s - bad packet length: %d\n",
 				__func__, length+2);

include/linux/usb.h

@@ -1178,7 +1178,7 @@ struct urb {
 	void *transfer_buffer;		/* (in) associated data buffer */
 	dma_addr_t transfer_dma;	/* (in) dma addr for transfer_buffer */
 	u32 transfer_buffer_length;	/* (in) data buffer length */
-	int actual_length;		/* (return) actual transfer length */
+	u32 actual_length;		/* (return) actual transfer length */
 	unsigned char *setup_packet;	/* (in) setup packet (control only) */
 	dma_addr_t setup_dma;		/* (in) dma addr for setup_packet */
 	int start_frame;		/* (modify) start frame (ISO) */