Avoid freeing the last request while it is being processed. This can
happen in some cases if reg_work is kicked for some reason while the
currently pending request is in flight.

Cc: Sander Eikelenboom <linux@eikelenboom.it>
Tested-by: NEliad Peller <eliad@wizery.com>
Tested-by: NColleen Twitty <colleen@cozybit.com>
Signed-off-by: NArik Nemtsov <arik@wizery.com>
Signed-off-by: NLuis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>