system_dlkm: Fix flag for mount point guard

Replace /system_dlkm mount guard flga from
BOARD_USES_SYSTEM_DLKM_PARTITION to
BOARD_USES_SYSTEM_DLKMIMAGE. board_config.mk
and other tools are using this format of image
name to auto generate code to prevent duplication.

Bug: 200082547
Test: TH
Signed-off-by: Ramji Jiyani <ramjiyani@google.com>
Change-Id: Ie4dc899509cf42afb553936e6dbf69d5ce234d01
diff --git a/rootdir/Android.mk b/rootdir/Android.mk
index ce2ec0e..b12594a 100644
--- a/rootdir/Android.mk
+++ b/rootdir/Android.mk
@@ -110,7 +110,8 @@
 ifdef BOARD_USES_METADATA_PARTITION
   LOCAL_POST_INSTALL_CMD += ; mkdir -p $(TARGET_ROOT_OUT)/metadata
 endif
-ifdef BOARD_USES_SYSTEM_DLKM_PARTITION
+ifdef BOARD_USES_SYSTEM_DLKMIMAGE
+  # /system_dlkm mount point
   LOCAL_POST_INSTALL_CMD += ; mkdir -p $(TARGET_ROOT_OUT)/system_dlkm
 endif