MIPS: Use USE_OF as the guard for appended dtb

Since OF is now a user selectable symbol, the choice for appended dtb
support should only be visible when USE_OF is selected, as this
indicates actual machine support for device tree in MIPS.
Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: Kevin Cernekee <cernekee@gmail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: John Crispin <blogic@openwrt.org>
Cc: Ganesan Ramalingam <ganesanr@broadcom.com>
Cc: Jayachandran C <jchandra@broadcom.com>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: James Hartley <james.hartley@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/11283/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -2705,7 +2705,7 @@ config BUILTIN_DTB
 	bool
 
 choice
-	prompt "Kernel appended dtb support" if OF
+	prompt "Kernel appended dtb support" if USE_OF
 	default MIPS_NO_APPENDED_DTB
 
 	config MIPS_NO_APPENDED_DTB