staging: wilc1000: fix variable signedness

txq_count receives a value from wilc_wlan_handle_txq()
and therefore should be u32

found using sparse:
drivers/staging/wilc1000/linux_wlan.c:306:58: warning:
 incorrect type in argument 2 (different signedness)

Signed-off-by: Ilia Sergachev <ilia.sergachev@unibas.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>