app/eventdev: fix possible uninitialized variable
app/eventdev: fix possible uninitialized variable

When compiling with -O1, this error can appear:
	app/test-eventdev/test_pipeline_common.c:332:6: error:
	‘ret’ may be used uninitialized in this function

If there is no device, then ret is returned without being initialized.
It is fixed by setting 0 as initial value.

Fixes: 032a965a8f1d ("app/eventdev: support Tx adapter")

Signed-off-by: Thomas Monjalon <5f50a84c1fa3bcff146405017f36aec1a10a9e38@monjalon.net>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk