msm: ion: Fix NULL pointer dereference in error path

If the hypervisor fails to assign the correct vmids to the
memory allocated, we should free the allocated memory. However
the free path depends on certain parameters of the ion_buffer
structure which have not yet been populated.

Update the function definition to accept the scatter gather list
instead of the ion buffer, since we are zero'ing the list
and not the buffer.

Change-Id: I68bef3af6c1b7e8092fbc0e878d3c825580f438e
Signed-off-by: Neeti Desai <neetid@codeaurora.org>