staging: rtl8188eu: change return type of rtw_hal_xmit()

The function rtw_hal_xmit() 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>