msm: kgsl: Handle missed alloc error cases

There is a chance that we could fail to allocate memory and then write
to it when allocating entries for our scatter gather list.  Handle the
error cases properly to prevent writing to NULL.

Change-Id: I33978ff53114ede7007b3240406583bcbef2f292
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>
Signed-off-by: Rajeev Kulkarni <krajeev@codeaurora.org>