pldmd: fix memory leak

`pldmTransport.recvMsg` in `pldmd` will call
`pldm_transport_af_mctp_recv` in libpldm. This function allocates memory
of `requestMsg` and copy the MCTP request message data to `requestMsg`.
`pldmd` should free memory of requestMsg after using.

Tested:
1. Check the memory usage of `pldmd`. There is no memory leak.

Signed-off-by: Thu Nguyen <thu@os.amperecomputing.com>
Change-Id: Ie9270509e60790618c1a399fa3c9bf34f6f54907
diff --git a/pldmd/pldmd.cpp b/pldmd/pldmd.cpp
index 7b932fa..21e2933 100644
--- a/pldmd/pldmd.cpp
+++ b/pldmd/pldmd.cpp
@@ -365,6 +365,8 @@
             warning("Failed to receive PLDM request: {RETURN_CODE}",
                     "RETURN_CODE", returnCode);
         }
+        /* Free requestMsg after using */
+        free(requestMsg);
     };
 
     bus.attach_event(event.get(), SD_EVENT_PRIORITY_NORMAL);