Revert "brcmfmac: Use atomic functions for intstatus update."

This reverts commit c98db0be.

The function atomic_set_mask() is not architecture independent
so it can not be used in the driver as is.

Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>