soc: qcom: glink: Update to avoid invalid pointer access

Invalid pointer access happens if invalid edge name is passed to the find
transport function.

Update find transport function to avoid invalid pointer access and return
proper error in case of invalid edge name.

Change-Id: I7d14e73f438ef3e055c5d3251c8e2b2e1beacada
Signed-off-by: Atish Kumar Patra <apatra@codeaurora.org>