cw1200: Fix up a large pile of sparse warnings

Most of these relate to endianness problems, and are purely cosmetic.

But a couple of them were legit -- listen interval parsing and some of
the rate selection code would malfunction on BE systems.

There's still one cosmetic warning remaining, in the (admittedly) ugly
code in cw1200_spi.c.  It's there because the hardware needs 16-bit SPI
transfers, but many SPI controllers only operate 8 bits at a time.

If there's a cleaner way of handling this, I'm all ears.

Signed-off-by: Solomon Peachy <pizza@shaftnet.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>