kernel: Deduplicate file paths in file_list.txt

This is a workaround for broken dirty rebuilds.

Test: breakfast gts4lvwifi && m && m
Change-Id: I2529efd0685f15eace5031df39e226dd5eaca1e8

build/tasks/kernel.mk

@@ -391,7 +391,8 @@ define build-image-kernel-modules-lineage
         for MODULE in $(1); do \
             BASENAME=$$(basename $$MODULE); \
             echo lib/modules$(6)/"$$BASENAME" >> "$(7)"; \
-        done \
+        done; \
+        sort -u "$(7)" -o "$(7)"; \
     fi;
 endef