msm: kgsl: Do not attempt recovery if context is detached

If the context is already detached no need to try recovery,
invalidate the context and free remaining commands from this
context.

Change-Id: If6280ae0016b4eb1e38f5cb0b88e2ba48a1fc70a
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>