libertas: remove casts from lbs_cmd() and lbs_cmd_with_response() macros

If stupid people like me give it arguments with the wrong type (like a
pointer to the structure, for example, instead of the structure itself),
then we should probably notice that at compile time. Otherwise, much
confusion ensues.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>