staging: r8188eu: clean up spacing style issues in core/rtw_xmit.c

Clean up spacing style issues in core/rtw_xmit.c reported by checkpatch.

CHECK: spaces preferred around that ...
WARNING: space prohibited between function name and open parenthesis '('
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210816155818.24005-20-straube.linux@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>