rtlwifi: rtl8192cu: Fix memset/memcpy 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>
Signed-off-by: John W. Linville <linville@tuxdriver.com>