staging: wilc1000: txq_event: Fix coding error

Fix incorrect usage of completion interface by replacing
'wait_for_completion' with 'complete'. This error was introduced
accidentally while replacing semaphores with mutexes.

Reported-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Binoy Jayan <binoy.jayan@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>