staging: brcm80211: reduce sparse messages on brcmsmac sources

Running sparse over the driver sources showed 1356 sparse messages
and quite a number are due to missing __iomem attribute in some
places. This patch reduces the number significantly.

Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>