brcmfmac: rename brcmf_sdio_buffrw()

The function brcmf_sdio_buffrw() is intended to be used for
transfering list of packets using scatter-gather functionality.
Rename function to brcmf_sdio_sglist_rw() to clarify this.

Reviewed-by: Franky Lin <frankyl@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>