coresight: tgu: Fix issue which is unable to enable/disable tgu

pm_runtime_get_sync can return positive. Correct the check of it.
Remove the extra spin_unlock and TGU_LOCK in enable_tgu.

Change-Id: I613269ea73f52c8ec5f4c986edcb102bbd14f843
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>