usb: gadget: add missing #include's

When #include'd alone, <linux/usb/gadget.h>
causes a lot of compilation errors and warnings
-- all because it relies on the including code to
bring in the necessary #include's instead of
doing this itself.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/usb/gadget.h

@@ -15,7 +15,12 @@
 #ifndef __LINUX_USB_GADGET_H
 #define __LINUX_USB_GADGET_H
 
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/list.h>
 #include <linux/slab.h>
+#include <linux/types.h>
 #include <linux/usb/ch9.h>
 
 struct usb_ep;