brcmfmac: rename brcmf_sdiod_buff_{read,write}() functions

Rename functions to brcmf_sdio_skbuff_{read,write}() as we pass an
skbuff to this function.

Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>