tahvo-usb: compile fix usb/gadget.h

Fix tahvo-usb.c header from include/linux/usb_gadget.h to
include/linux/usb/gadget.h.
drivers/cbus/tahvo-usb.c:37:30: linux/usb_gadget.h: No such file or directory
Signed-off-by: Francisco Alecrim <francisco.alecrim@indt.org.br>
Signed-off-by: Tony Lindgren <tony@atomide.com>

drivers/cbus/tahvo-usb.c

@@ -34,7 +34,7 @@
 #include <linux/interrupt.h>
 #include <linux/platform_device.h>
 #include <linux/usb/ch9.h>
-#include <linux/usb_gadget.h>
+#include <linux/usb/gadget.h>
 #include <linux/usb.h>
 #include <linux/usb/otg.h>
 #include <linux/i2c.h>