bnx2: In bnx2_set_mac_link() return void rather then int

bnx2_set_mac_link() doesn't need to return any error codes.  And
all the callers don't check the return code. It is safe to
change the return type to a void.

Signed-off-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Acked-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>