staging: rtl8188eu: use __func__ instead of hardcoded name - style

Use __func__ instead of hardcoded function name in rtw_xmit_entry().
Reported by checkpatch.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>