libertas: endianness fixes

Recently I found that that sparse by default doesn't endianness
checks. So I changed my compilation habit to be

make modules C=1 SUBDIRS=drivers/net/wireless/libertas
CHECKFLAGS="-D__CHECK_ENDIAN__"

so that I get the little-endian checks from sparse as well. That
showed up a good bunch of problems.

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>