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

pm_runtime_get_sync can return positive. Correct the check of it.
And remove the extra spin_unlock in enable_tgu which will cause issue
when disable tgu.

Change-Id: Ic8b46d1da7cbfe06b3e58e34bd1e62cea31ac8bf
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>