build_image: Increase spare inodes to 12.

Test: builds device with DAP
Change-Id: I816a7da54bbe23d4eb1140ac0d101c0fee175f0a
diff --git a/tools/releasetools/build_image.py b/tools/releasetools/build_image.py
index ad0432d..8712d85 100755
--- a/tools/releasetools/build_image.py
+++ b/tools/releasetools/build_image.py
@@ -78,7 +78,7 @@
   # increase by > 4% as number of files and directories is not whole picture.
   inodes = output.count('\n')
   spare_inodes = inodes * 4 // 100
-  min_spare_inodes = 8
+  min_spare_inodes = 12
   if spare_inodes < min_spare_inodes:
     spare_inodes = min_spare_inodes
   return inodes + spare_inodes