Fix syntax error in Makefile

When calling extract-avb-chain-public-keys method with
BOARD_CUSTOMIMAGES_PARTITION_LIST, syntax error leads to build failure.
Fix it by removing incorrect backslash.

Test: build with BOARD_CUSTOMIMAGES_PARTITION_LIST

Change-Id: I017244eac7ef0d04f67ba68412ec6a95cca2e302
Signed-off-by: Junki Lee <junki486.lee@lge.com>
diff --git a/core/Makefile b/core/Makefile
index 02deadd..f38f3a0 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -4919,7 +4919,7 @@
   $(if $(BOARD_AVB_CUSTOMIMAGES_PARTITION_LIST),\
     $(hide) $(foreach partition,$(BOARD_AVB_CUSTOMIMAGES_PARTITION_LIST), \
         $(AVBTOOL) extract_public_key --key $(BOARD_AVB_$(call to-upper,$(partition))_KEY_PATH) \
-            --output $(1)/$(partition).avbpubkey;)) \
+            --output $(1)/$(partition).avbpubkey;))
   $(if $(BOARD_AVB_VBMETA_CUSTOM_PARTITIONS),\
     $(hide) $(foreach partition,$(BOARD_AVB_VBMETA_CUSTOM_PARTITIONS), \
         $(AVBTOOL) extract_public_key --key $(BOARD_AVB_VBMETA_$(call to-upper,$(partition))_KEY_PATH) \