brcmfmac: Remove func0 from function array

func0 is not provided by the mmc stack as a function when probing.
Instead providing specific access functions to read/write it.

This prepares for a patch to remove the actual array entry itself.

Signed-off-by: Ian Molton <ian@mnementh.co.uk>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
[arend: rephrased the commit message]
[arend: removed unrelated comment for which separate patch is warranted]
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>