arm: am335x: siemens board use in DFU mode fullspeed only

Siemens boards are now using DFU in fullspeed only. For
this CONFIG_USB_GADGET_DUALSPEED is undefined.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Liu Bin <b-liu@ti.com>
Cc: Lukas Stockmann <lukas.stockmann@siemens.com>

include/configs/siemens-am33x-common.h

@@ -231,7 +231,7 @@
 #define CONFIG_MUSB_GADGET
 #define CONFIG_MUSB_PIO_ONLY
 #define CONFIG_MUSB_DISABLE_BULK_COMBINE_SPLIT
-#define CONFIG_USB_GADGET_DUALSPEED
+#undef CONFIG_USB_GADGET_DUALSPEED
 #define CONFIG_USB_GADGET_VBUS_DRAW	2
 #define CONFIG_MUSB_HOST