net: typhoon: Remove redundant casts

Both image_data and typhoon_fw->data are const u8*, so the cast to u8*
is unnecessary and confusing.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: David Dillow <dave@thedillows.org>
Signed-off-by: David S. Miller <davem@davemloft.net>