msm: npu: Allocate buffer per client for register read

In order to avoid double free or use after free the buffer
allocated while reading registers, it is needed to allocate the
buffer per client and free it in release function.

Change-Id: Ida806933819a6070164948e8abe034c41f8548fd
Signed-off-by: Jilai Wang <jilaiw@codeaurora.org>