slimbus: slim-msm: Fix QMI response handler

If a QMI transaction times out and the response arrives at a later time,
QMI framework creats a dummy transaction and invokes the response handler.
Signaling using the dummy transaction leads to a crash.

Check if the transaction handle is a valid one before using it to signal
the waiter.

CRs-Fixed: 2207453
Change-Id: I114bf89beb430e748687cb862900dbba8c4b3b3a
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>