brcmfmac: remove brcmf_sdio_regrw_helper() from header file

Make brcmf_sdio_regrw_helper() static removing its use outside of
the bcmsdh.c source file.

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>

diff --cc drivers/net/wireless/brcm80211/brcmfmac/bcmsdh.c
Simple merge

diff --cc drivers/net/wireless/brcm80211/brcmfmac/dhd_sdio.c
Simple merge

diff --cc drivers/net/wireless/brcm80211/brcmfmac/sdio_host.h
Simple merge