staging:rtl8188eu Fix use __func__ for function name

This patch fixes the WARNING: Prefer using '"%s...", __func__' to using
this function's name, in a string

Signed-off-by: Janani Sankara Babu <jananis37@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>