USB: usbtmc: Use explicit unsigned type for input buffer instead of char*

Silences compiler warning about comparison with 0x80, and type now matches the
corresponding _bulk_out function.

drivers/usb/class/usbtmc.c: In function ‘usbtmc_ioctl_abort_bulk_in’:
drivers/usb/class/usbtmc.c:163: warning: comparison is always false due to limited range of data type
Signed-off-by: Chris Malley <mail@chrismalley.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/class/usbtmc.c

@@ -133,7 +133,7 @@ static int usbtmc_release(struct inode *inode, struct file *file)
 
 static int usbtmc_ioctl_abort_bulk_in(struct usbtmc_device_data *data)
 {
-	char *buffer;
+	u8 *buffer;
 	struct device *dev;
 	int rv;
 	int n;