msm: ocmem: Check for NULL pointer from get_zone

The get_zone function might return NULL if it is
unable to find the zone for the associated client
id. Add check to prevent NULL pointer dereferencing.

Signed-off-by: Neeti Desai <neetid@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
msm: ocmem: Add NULL pointer check for req structure

BUG_ON if req structure returned from handle_to_req
returns a NULL pointer.

Signed-off-by: Neeti Desai <neetid@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>