staging: comedi: ni_usb6501: 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: NIan Abbott <abbotti@mev.co.uk>
Reviewed-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_usb6501.c

@@ -96,9 +96,8 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/slab.h>
-#include <linux/usb.h>
 
-#include "../comedidev.h"
+#include "../comedi_usb.h"
 
 #define	NI6501_TIMEOUT	1000