hostap: Fix build warnings

Using "%02x" needs an unsigned integer, but all MAC addresses use
"unsigned char/char" as the data type, so, to avoid warnings, use a
temporary array.

Also, the macro from the WPA supplicant doesn't use the address of the
array element and causes warnings, so re-define the macro with address
of the element.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>