staging: brcm80211: simpler string handling in brcmf_c_pktfilter_offload_set()

Replaced two functions with strcpy().

Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>