Always define sdk_addon as phony

dist-write-files will add dist targets to the sdk_addon target,
but the sdk_addon target is not declared as phony when building
with mm (ONE_SHOT_MAKEFILE set), causing:
build/make/core/main.mk:1495: error: writing to readonly directory: "sdk_addon"

Always define sdk_addon as phony even if ONE_SHOT_MAKEFILE is set.

Bug: 118144231
Test: mm
Change-Id: I99d14a98a7597ebd694c765f94b0d6f4486860dc
diff --git a/core/tasks/sdk-addon.mk b/core/tasks/sdk-addon.mk
index 93fea4e..122161b 100644
--- a/core/tasks/sdk-addon.mk
+++ b/core/tasks/sdk-addon.mk
@@ -12,10 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-ifndef ONE_SHOT_MAKEFILE
-
 .PHONY: sdk_addon
 
+ifndef ONE_SHOT_MAKEFILE
+
 # If they didn't define PRODUCT_SDK_ADDON_NAME, then we won't define
 # any of these rules.
 addon_name := $(strip $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SDK_ADDON_NAME))