memshare: Release the memory only if no allocation is done

Currently, memshare relies on the system monitor only for
releasing memory for the allocated clients. It may happen that
XPU is still intact on the modem side while driver tries to
release the memory. This patch ensures that memory release only
happens if XPU is released.

Change-Id: I45716c0abe6bc08559854782ff73a332e148a7cb
Signed-off-by: Katish Paran <kparan@codeaurora.org>