tests: drop -d option from ffserver invocation

It randomly causes failures with an error like:
"Failed to set value '-f' for option 'd': Error number -920332800 occurred"

(The error number is different every time.)
Reviewed-by: Reynaldo H. Verdejo Pinochet <reynaldo@osg.samsung.com>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

tests/ffserver-regression.sh

@@ -12,7 +12,7 @@ target_path=$5
 FILES=$(sed -n 's/^[^#]*<Stream \(.*\)>.*/\1/p' $2 | grep -v html)
 
 rm -f tests/feed1.ffm
-$target_exec ${target_path}/ffserver${PROGSUF} -d -f "$2" &
+$target_exec ${target_path}/ffserver${PROGSUF} -f "$2" &
 FFSERVER_PID=$!
 echo "Waiting for feeds to startup..."
 sleep 2