staging: rtl8192u: remove cmpk_message_handle_tx()

The function cmpk_message_handle_tx() is called only in r8192U_dm.c in two
places. The first call resides outside an #ifdef RTL8192U guard, and since
RTL8192U is defined this call can be removed. At the other site this function
is called, there is no check on its return value. Since cmpk_message_handle_tx()
does not do anything else other than returning true, it can be safely removed.

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>