brcmfmac: fix SDIO access for big-endian host

These full-mac chips use little-endian byte ordering. This patch
adds a few missing conversions to/from little-endian so that the
driver may be used with a big-endian host.

Signed-off-by: Remi Depommier <rde@setrix.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201020174639.28892-1-rde@setrix.com