staging: brcm80211: remove several externs from dhd_linux.c

The script checkpatch.pl flagged for some extern variables in
dhd_linux.c source. Several have been fixed in this patch. Two
remaining are in macro conditional code that needs cleanup so
they are not resolved here.

Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>