staging: r8712u: use is_zero_ether_addr() instead of memcmp()
Using is_zero_ether_addr() instead of directly use
memcmp(addr, "\x00\x00\x00\x00\x00\x00", ETH_ALEN)
to determine if the ethernet address is all zeros.
spatch with a semantic match is used to found this problem.
(http://coccinelle.lip6.fr/)