staging: rtl8188eu: change return type of rtl8188eu_xmitframe_complete()

The function rtl8188eu_xmitframe_complete() returns true or false.
Change the return type from s32 to bool.

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