coresight: release tpiu regulator of node only when done using it

Currently TPIU regualtor DT of node gets released on encountering
errors while reading voltage or current levels which can cause
use after free issues. Ensure the regulator of node gets released
only when we are completely done using it.

Change-Id: Ifaf8469aedb77e7d9fc6f71dab99417414f4e88d
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>