staging: brcm80211: fix 'uninitialized usage' compiler warning

Building for the ARM resulted in a compiler warning about usage of
a possibly uninitialized variable. The warning is valid and the
code has been fixed accordingly.

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