brcmfmac: Fix incorrect type in assignment

The left-hand side of the assignment from cpu_to_le32() should be of
type __le32. This commit clears the warning reported by sparse when
building with C=1 CF="-D__CHECK_ENDIAN__".

Fixes: d56fd83c ("brcmfmac: fix SDIO access for big-endian host")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Remi Depommier <rde@setrix.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201116001639.31958-1-rde@setrix.com