brcmfmac: Remove dead IO code

The value passed to brcmf_sdiod_addrprep() is *always* 4
remove this parameter and the unused code to handle it.

Signed-off-by: Ian Molton <ian@mnementh.co.uk>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>