brcmfmac: fix sparse warning introduced with checkdied patch

The commit "brcmfmac: introduce checkdied debugfs functionality"
also introduced a sparse warning:

..../brcmfmac/dhd_sdio.c:3147:45: sparse: cast to restricted __le32

This patch fixes this sparse warning.

Reported-by: Fengguang Wu <wfg@linux.intel.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>