bnx2x: Remove read_status_t function casts

The function casts for .read_status callbacks end up casting some int
return values to u8. This seems to be bug-prone (-EINVAL being returned
into something that appears to be true/false), but fixing the function
prototypes doesn't change the existing behavior. Fix the return values
to remove the casts.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>