memshare: Response to modem in case of memory allocation failure

Currently memshare driver doesn't respond back in case of memory
allocation failure on apps side. This patch resolves the issue
and sends appropriate response for all cases.

Change-Id: Iab58b38108a592e73ebf9d438daffee5722bdfcd
CRs-Fixed: 681146
Signed-off-by: Katish Paran <kparan@codeaurora.org>