char: remove use-after-free on win-stdio

Found by reviewing the code, win_stdio_close() is called by
qemu_chr_free() which then call qemu_chr_free_common() taking care of
freeing CharDriverState*.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20161022095318.17775-3-marcandre.lureau@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

qemu-char.c

@@ -2435,7 +2435,6 @@ static void win_stdio_close(CharDriverState *chr)
     }
 
     g_free(chr->opaque);
-    g_free(chr);
 }
 
 static CharDriverState *qemu_chr_open_stdio(const char *id,