staging: rtl8723au: Use __func__ in trace logs

Rework the trace log-related lines in rtl8723au's rtw_security.c
to use the __func__ GCC magic variable instead of hardcoding the
function names into the trace log strings. This also corrects a
copy-paste-related typo in the function named rtw_tkip_decrypt23a.

Thanks to Jes Sorensen for the suggestion to use __func__.

Signed-off-by: M. Vefa Bicakci <m.v.b@runbox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>