sepolicy: Fix denails for flash_recovery service

Needed when option is checked to update cm recovery

Change-Id: I0b2fbfd7c141ae03ce14b9afeffd3a027d791c80
diff --git a/sepolicy/system_server.te b/sepolicy/system_server.te
new file mode 100644
index 0000000..4728a44
--- /dev/null
+++ b/sepolicy/system_server.te
@@ -0,0 +1,2 @@
+allow system_server recovery_cache_file:dir rw_dir_perms;
+allow system_server recovery_cache_file:file create_file_perms;