staging: wilc1000: remove pstrWFIDrv in host_int_remove_key

This patch remove pstrWFIDrv in host_int_remove_key. There is no need to
make another variable to check if first argument is NULL or not.
It is able to use wfi_drv directly that is first argument of this
function.

Signed-off-by: Chaehyun Lim <chaehyun.lim@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>