msm: kgsl: fix infinite loop in adreno_find_region()

If postmortem dump tried to parse a context switch
buffer for any context except the current context
this function would never return.

Change-Id: I19f2fe7afda5796180cdf5f81c17fad960e84f05
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>