brcmsmac: Replace kmalloc/memset with kzalloc

In ai_attach(), space is allocated for an si_info struct. Immediately
after the allocation, routine ai_doattach() is called and that allocated
space is set to zero. As no other routine calls ai_doattach(), kzalloc()
can be utilized.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Acked-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>