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

It is possible that notify call is called after etr is disabled or
after mode switch from usb to etr. Add etr status check to avoid
exception.

Change-Id: I65e81e5ec01ebb3747936cdd81f886632c5419f1
Signed-off-by: Tao,Zhang <taozha@codeaurora.org>