migration: fix pfd leak

Fix leak spotted by ASAN:

Direct leak of 16 byte(s) in 1 object(s) allocated from:
    #0 0x7fe1abb80a38 in __interceptor_calloc (/lib64/libasan.so.4+0xdea38)
    #1 0x7fe1aaf1bf75 in g_malloc0 ../glib/gmem.c:124
    #2 0x7fe1aaf1c249 in g_malloc0_n ../glib/gmem.c:355
    #3 0x55f4841cfaa9 in postcopy_ram_fault_thread /home/elmarco/src/qemu/migration/postcopy-ram.c:596
    #4 0x55f48479447b in qemu_thread_start /home/elmarco/src/qemu/util/qemu-thread-posix.c:504
    #5 0x7fe1a043550a in start_thread (/lib64/libpthread.so.0+0x750a)

Regression introduced with commit 00fa4fc.

Signed-off-by: Marc-André Lureau <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Peter Xu <[email protected]>
Signed-off-by: Dr. David Alan Gilbert <[email protected]>

migration/postcopy-ram.c

@@ -754,6 +754,7 @@ static void *postcopy_ram_fault_thread(void *opaque)
         }
     }
     trace_postcopy_ram_fault_thread_exit();
+    g_free(pfd);
     return NULL;
 }