staging: wilc1000: fix const cast warnings

The wilc1000 driver produces a lot of warnings about invalid
casts between const and non-const variables. This reworks
the code to avoid all those warnings, by marking variables
and function arguments const.

A lot of the types use WILC_Uint8, I change them to const u8
for style reasons, as I'm touching them anyway.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>