CA Certs: Modify object entry path to fix object sub-tree hierarchy

Currently there is no interface added signal generated as object
path is not following hierarchy.

to fix this behaviour, this commit modifies object entry path
to /xyz/openbmc_project/certs/ca/entry/<id>
InterfacesAdded signal:

signal time=1619111735.917791 sender=:1.660 -> destination=(null destination)
 serial=68 path=/xyz/openbmc_project/certs/ca; interface=org.freedesktop.DBus.ObjectManager;
  member=InterfacesAdded
   object path "/xyz/openbmc_project/certs/ca/entry/6"

Tested by:
D-bus monitor while Creating dbus objects

Signed-off-by: Ravi Teja <raviteja28031990@gmail.com>
Change-Id: I3ce8aa2b2ec5da321557ea40f484ea2947d57442
diff --git a/bmc-vmi-ca/ca_certs_manager.cpp b/bmc-vmi-ca/ca_certs_manager.cpp
index f6622ff..3b11a53 100644
--- a/bmc-vmi-ca/ca_certs_manager.cpp
+++ b/bmc-vmi-ca/ca_certs_manager.cpp
@@ -13,7 +13,6 @@
 {
 namespace cert
 {
-static constexpr auto objectEntry = "/xyz/openbmc_project/certs/entry";
 static constexpr auto maxCertSize = 4096;
 namespace fs = std::filesystem;
 using namespace phosphor::logging;
@@ -33,7 +32,7 @@
                                   Argument::ARGUMENT_VALUE(csr.c_str()));
         }
         auto id = lastEntryId + 1;
-        objPath = fs::path(objectEntry) / std::to_string(id);
+        objPath = fs::path(OBJPATH) / "ca" / "entry" / std::to_string(id);
         std::string cert;
         // Creating the dbus object here with the empty certificate string
         // actual signing is being done by the hypervisor, once it signs then