msm: kgsl: Make the snapshot dumper more tolerant of corrupted IBs

If there are a lot of sequential commands in the ringbuffer for the
same context there is a high probablity that some of the memory
for the older commands has been reused and so the contents may not
be reliable. Increase robustness by making sure we don't parse the
same IB over and over again and be more tolerant of errors and
strange sizes.

Change-Id: Ic0dedbade8504ea258ceea40593cb75e7d6211c8
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>