wilc1000: Fix spurious "FW not responding" error

When deinitializing the driver, one or more "FW not responding" error
appears on the console.  This appears to be due to wilc_wlan_stop()
disabling host/WILC1000 communication, but then right afterwards, it
tries to release the bus with chip-sleep enabled.  The problem is
enabling the chip-sleep cannot success once host/WILC1000
communication is disabled.  Fix by only releasing the bus.

Signed-off-by: David Mosberger-Tang <davidm@egauge.net>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211208062747.3405221-1-davidm@egauge.net