usb: gadget: move USB_BUFSIZ into global composite.h

This patch moves USB_BUFSIZ into global header file as
USB_COMP_EP0_BUFSIZ. There is currently only one user (f_sourcesink)
besides composite which need it. Ideally f_sourcesink would have its
own ep0 buffer. Lets keep it that way it was for now.

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/f_sourcesink.c b/drivers/usb/gadget/f_sourcesink.c
index 5c1b68b..3c126fd 100644
--- a/drivers/usb/gadget/f_sourcesink.c
+++ b/drivers/usb/gadget/f_sourcesink.c
@@ -795,7 +795,7 @@
 	u16			w_value = le16_to_cpu(ctrl->wValue);
 	u16			w_length = le16_to_cpu(ctrl->wLength);
 
-	req->length = USB_BUFSIZ;
+	req->length = USB_COMP_EP0_BUFSIZ;
 
 	/* composite driver infrastructure handles everything except
 	 * the two control test requests.