staging: rtl8712: Fix checkpatch.pl warning

WARNING: Avoid multiple line dereference - prefer 'param->u.crypt.key'

Signed-off-by: Alexander Mikhalevich <alex.mikhalevich@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>