coresight: tmc: Verify Coresight TMC device before accessing it

reset_source_sink_store can race with tmc_open/release call. In
such cases, reset_source_sink_store will disable the sink in its
path and tmc_open/release try to access it in the disabled state.
Avoid this by verifying the corresponding coresight device state.

Change-Id: I9e8aa0171af14762ed10ca30a80b43f4132e847d
Signed-off-by: Yadu MG <ymg@codeaurora.org>