msm: kgsl: Do not purge non-overlapping freemem list entries

A freemem list entry maybe truncated/deleted even if it doesn't
overlap with a new buffer, for example, if the new buffer is entirely
to the left or right of the entry. Fix the conditional logic so
that an entry may be truncated/deleted only if it overlaps with
the new buffer.

Change-Id: Ib1519f20d3b56c1e0ed36e9e0afb33c1b31d6166
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>