memshare: Do not overwrite the response for the failure case

Currently the driver send success response value even in the
case of failure. This patch resolves that issue. Also it handles
one incorrect mutex handling for memory failure case.

Change-Id: Ie3a6570fac6969826e69fdd9e72c01aa98a0c995
Signed-off-by: Katish Paran <kparan@codeaurora.org>