staging: agnx, fix bssid compiler warnings

conf->bssid is const. Propagate const to not get compiler warnings:
agnx/pci.c: In function ‘agnx_config_interface’:
agnx/pci.c:319: warning: passing argument 2 of ‘agnx_set_bssid’ discards qualifiers from pointer target type
agnx/pci.c:321: warning: passing argument 2 of ‘hash_write’ discards qualifiers from pointer target type

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>