staging: comedi: dt9812: include new "comedi_usb.h" header

Include the new "../comedi_usb.h" header instead of <linux/usb.h> and
"../comedidev.h", which will now get included indirectly.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/dt9812.c

@@ -42,9 +42,8 @@ for my needs.
 #include <linux/module.h>
 #include <linux/errno.h>
 #include <linux/uaccess.h>
-#include <linux/usb.h>
 
-#include "../comedidev.h"
+#include "../comedi_usb.h"
 
 #define DT9812_DIAGS_BOARD_INFO_ADDR	0xFBFF
 #define DT9812_MAX_WRITE_CMD_PIPE_SIZE	32