staging: wilc1000: use short names to fix over 80 issue in tcp_process()

Use short variable names to avoid line over 80 chars checkpatch warning
in tcp_process().

struct pending_acks_info     --> struct pending_ack
int tcp_pending_ack_idx      --> int ack_idx
u32 pending_ack              --> u32 pending_ack_idx

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>