msm: kgsl: Add a missing refcount put for kgsl_context

Fix a potential memory leak by putting in the missing kgsl_context_put()
in fault trace detect.

Change-Id: Ic0b43c831a88ac3e45bbe484bde843b46b6f09f6
Signed-off-by: Harsh Vardhan Dwivedi <hdwivedi@codeaurora.org>