USB: Add EXPORT_SYMBOL for usb_alloc_dev

usb_alloc_dev is used by lvstest driver now which can be built as
module. Therefore export usb_alloc_dev symbol.

Signed-off-by: Pratyush Anand <pratyush.anand@st.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index 4d11449..2dd2362 100644
--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -501,6 +501,7 @@
 	}
 	return dev;
 }
+EXPORT_SYMBOL_GPL(usb_alloc_dev);
 
 /**
  * usb_get_dev - increments the reference count of the usb device structure