sunxi: Fix USB_GADGET implication

USB_GADGET will fail to compile if USB_MUSB_GADGET is not defined. Make
sure we have that condition right.

Fixes: e0ea88042d51 ("sunxi: Imply USB_ETHER")
Suggested-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

arch/arm/Kconfig

@@ -704,7 +704,6 @@ config ARCH_SUNXI
 	imply SPL_MMC_SUPPORT if MMC
 	imply SPL_POWER_SUPPORT
 	imply SPL_SERIAL_SUPPORT
-	imply USB_ETHER
 	imply USB_GADGET
 
 config TARGET_TS4600

drivers/usb/gadget/Kconfig

@@ -138,6 +138,7 @@ endif # USB_GADGET_DOWNLOAD
 
 config USB_ETHER
 	bool "USB Ethernet Gadget"
+	default y if ARCH_SUNXI && USB_MUSB_GADGET
 	help
 	  Creates an Ethernet network device through a USB peripheral
 	  controller. This will create a network interface on both the device