staging: brcm80211: code cleanup

Removed inactive code sections (BCM_DMAPAD and CHIPC_UART_ALWAYS_ON
were never defined). Also replaced magic number by #define. Deleted
incorrect comment.

Signed-off-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>