bnx2x: Drop redundant callback function casts

NULL is already "void *" so it will auto-cast in assignments and
initializers. Additionally, all the callbacks for .link_reset,
.config_loopback, .set_link_led, and .phy_specific_func are already
correct. No casting is needed for these, so remove them.
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>