staging: wilc1000: wilc_wlan: Remove wrapper function

Remove is_tcp_ack_filter() which only returns the value of boolean
variable `enabled` by replacing the only call site with the variable
`enabled` itself.

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>