staging: wilc1000: remove function pointer wlan_add_to_tx_que

This patch removes function pointer wlan_add_to_tx_que and just call
the function wilc_wlan_txq_add_net_pkt. Remove static from the function also.

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Tony Cho <tony.cho@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>