staging: wilc1000: use g_linux_wlan->txq_spinlock not the pointer of it

Use spinlock variable g_linux_wlan->txq_spinlock itself instead of
g_wlan.txq_spinlock which is pointer of g_linux_wlan->txq_spinlock.
Delete os_context.txq_spin_lock, g_wlan.txq_spinlock and it's related codes.

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