staging: wilc1000: avoid mutex unlock without lock in wilc_wlan_handle_txq()

In wilc_wlan_handle_txq(), mutex unlock was called without acquiring
it. Also error code for full VMM condition was incorrect as discussed in
[1]. Now used a proper code to indicate VMM is full, for which transfer
to VMM is required again. 'wilc_wlan_handle_txq()' should be called
again if the VMM space was full earlier or otherwise based on
'txq_event' signal.

1. https://lore.kernel.org/driverdev-devel/20191113183322.a54mh2w6dulklgsd@kili.mountain/



Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Link: https://lore.kernel.org/r/20200123182129.4053-2-ajay.kathat@microchip.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>