msm: kgsl: Fix the element ordering for kgsl_gpumem_sync_cache_compat

In comparison to the main struct kgsl_gpumem_sync_cache, the
length and offset elements were flipped for the equivalent compat
struct. This causes problems since the fields populated by
userspace now have the wrong values and we do things incorrectly
with these values.

CRs-Fixed: 663677
Change-Id: I6bac08676baf43909371270cbf9567d26567b974
Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>