rtl8192du: drop private endian framework

Build-tested on:
 - i386
 - x86_64
 - powerpc (qemu-system-ppc, Debian/unstable, kernel 3.8)

runtime-tested on:
 - i386
 - x86_64

Signed-off-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>