coresight: byte-cntr: Add ETR status check in bypass notifier

Add ETR status check while receiving USB_QDSS_CONNECT event.
Otherwise, there will cause crash due to NULL pointer issue.
Since ETR buffer will be released if ETR is disabled.

Change-Id: I358d25477c938844df5bff5c29ddbee307b770e3
Signed-off-by: Tao Zhang <taozha@codeaurora.org>