USB: gadget: composite: usb_string_ids_*() functions added

usb_string_ids_tab() and usb_string_ids_n() functions added to
the composite framework.  The first accepts an array of
usb_string object and for each registeres a string id and the
second registeres a given number of ids and returns the first.

This may simplify string ids registration since gadgets and
composite functions won't have to call usb_string_id() several
times and each time check for errer status -- all this will be
done with a single call.

Signed-off-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/include/linux/usb/composite.h b/include/linux/usb/composite.h
index 139353e..f378075 100644
--- a/include/linux/usb/composite.h
+++ b/include/linux/usb/composite.h
@@ -342,6 +342,10 @@
 };
 
 extern int usb_string_id(struct usb_composite_dev *c);
+extern int usb_string_ids_tab(struct usb_composite_dev *c,
+			      struct usb_string *str);
+extern int usb_string_ids_n(struct usb_composite_dev *c, unsigned n);
+
 
 /* messaging utils */
 #define DBG(d, fmt, args...) \