cil_write_ast.c: fix compile time error

Fix compile time error in Android specific code.

../cil/src/cil_write_ast.c: In function ‘__cil_write_node_helper’:
../cil/src/cil_write_ast.c:1156:17: error: variable ‘db’ set but not used [-Werror=unused-but-set-variable]
  struct cil_db *db = NULL;
                 ^~
../cil/src/cil_write_ast.c: In function ‘__cil_write_last_child_helper’:
../cil/src/cil_write_ast.c:1465:17: error: variable ‘db’ set but not used [-Werror=unused-but-set-variable]
  struct cil_db *db = NULL;
                 ^~

Test: compiles
Change-Id: I0af0e896ba1591ef43726dbee9906d581390e1f3
1 file changed