staging: brcm80211: use identifiers instead of string for srom lookup

The driver variables from srom are stored in memory with string
identifiers and the caller needed to use this string identifier
to retrieve a driver variable. The commit changes the calling
code replacing strings with enumerated identifiers.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>