build: avoid generating JSON info on missing image

Previously, build would fail for targets containing devices with not
initramfs image (such as mpc85xx-p1010). Only generate the JSON image
info for the initramfs image when we have one to avoid breaking the
builds.

Fixes commit d3140d052964 ("build/json: generate json file for initramfs")

Signed-off-by: David Bauer <[email protected]>

include/image.mk

@@ -472,8 +472,8 @@ endef
 ifndef IB
 define Device/Build/initramfs
   $(call Device/Export,$(KDIR)/tmp/$$(KERNEL_INITRAMFS_IMAGE),$(1))
-  $$(_TARGET): $$(if $$(KERNEL_INITRAMFS),$(BIN_DIR)/$$(KERNEL_INITRAMFS_IMAGE)) \
-	  $$(if $$(CONFIG_JSON_OVERVIEW_IMAGE_INFO), $(BUILD_DIR)/json_info_files/$$(KERNEL_INITRAMFS_IMAGE).json,)
+  $$(_TARGET): $$(if $$(KERNEL_INITRAMFS),$(BIN_DIR)/$$(KERNEL_INITRAMFS_IMAGE) \
+	  $$(if $$(CONFIG_JSON_OVERVIEW_IMAGE_INFO), $(BUILD_DIR)/json_info_files/$$(KERNEL_INITRAMFS_IMAGE).json,))
 
   $(KDIR)/$$(KERNEL_INITRAMFS_NAME):: image_prepare
   $(BIN_DIR)/$$(KERNEL_INITRAMFS_IMAGE): $(KDIR)/tmp/$$(KERNEL_INITRAMFS_IMAGE)