Append vendor kernel modules in mk file.

Append vendor kernel modules variable instead of overwriting it.
Otherwise, the global variables set by other board specific makefile
will be overwritten.

Test: Manual build and verify kernel module is appended correctly.
Bug: 260153425
Change-Id: I574be28ca6fd345ba717e424dd32eb6e30fb4f34
diff --git a/BoardConfig-common.mk b/BoardConfig-common.mk
index fa3d102..1e4400a 100644
--- a/BoardConfig-common.mk
+++ b/BoardConfig-common.mk
@@ -364,11 +364,11 @@
 BOARD_VENDOR_RAMDISK_KERNEL_MODULES := $(addprefix $(KERNEL_MODULE_DIR)/, $(BOARD_VENDOR_RAMDISK_KERNEL_MODULES_LOAD_EXTRA))
 BOARD_VENDOR_RAMDISK_KERNEL_MODULES += $(addprefix $(KERNEL_MODULE_DIR)/, $(notdir $(BOARD_VENDOR_RAMDISK_KERNEL_MODULES_LOAD_FILE)))
 
-BOARD_VENDOR_KERNEL_MODULES_LOAD := $(strip $(shell cat $(KERNEL_MODULE_DIR)/vendor_dlkm.modules.load))
+BOARD_VENDOR_KERNEL_MODULES_LOAD += $(strip $(shell cat $(KERNEL_MODULE_DIR)/vendor_dlkm.modules.load))
 ifndef BOARD_VENDOR_KERNEL_MODULES_LOAD
 $(error vendor_dlkm.modules.load not found or empty)
 endif
-BOARD_VENDOR_KERNEL_MODULES := $(KERNEL_MODULES)
+BOARD_VENDOR_KERNEL_MODULES += $(KERNEL_MODULES)
 
 # Using BUILD_COPY_HEADERS
 BUILD_BROKEN_USES_BUILD_COPY_HEADERS := true