staging: brcm80211: brcmfmac: Fix memset using sizeof(ptr) not sizeof(*ptr)

Found via coccinelle script

@@
type T;
T* ptr;
expression E1;
@@

* memset(E1, 0, sizeof(ptr));

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>