rtl8188eu: Simplify rtw_endofpktfile() in xmit_linux.c

scripts/checkpatch.pl reports a coding style problem in xmit_linux.c

  WARNING:BRACES: braces {} are not necessary for single statement blocks
  #61852: FILE: rtl8188eu/os_dep/xmit_linux.c:70:

This patch removes unnecessary braces and simplifies the function to a
single return statement.

Signed-off-by: Krzysztof Konopko <kris@konagma.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>