linux: don't use $ in dtb comment as the shell tries to expand them

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

linux/linux.mk

@@ -197,14 +197,14 @@ define LINUX_BUILD_DTB
 	$(TARGET_MAKE_ENV) $(MAKE) $(LINUX_MAKE_FLAGS) -C $(@D) $(KERNEL_DTBS)
 endef
 define LINUX_INSTALL_DTB
-	# dtbs moved from arch/$ARCH/boot to arch/$ARCH/boot/dts since 3.8-rc1
+	# dtbs moved from arch/<ARCH>/boot to arch/<ARCH>/boot/dts since 3.8-rc1
 	cp $(addprefix \
 		$(KERNEL_ARCH_PATH)/boot/$(if $(wildcard \
 		$(addprefix $(KERNEL_ARCH_PATH)/boot/dts/,$(KERNEL_DTBS))),dts/),$(KERNEL_DTBS)) \
 		$(BINARIES_DIR)/
 endef
 define LINUX_INSTALL_DTB_TARGET
-	# dtbs moved from arch/$ARCH/boot to arch/$ARCH/boot/dts since 3.8-rc1
+	# dtbs moved from arch/<ARCH>/boot to arch/<ARCH>/boot/dts since 3.8-rc1
 	cp $(addprefix \
 		$(KERNEL_ARCH_PATH)/boot/$(if $(wildcard \
 		$(addprefix $(KERNEL_ARCH_PATH)/boot/dts/,$(KERNEL_DTBS))),dts/),$(KERNEL_DTBS)) \