msm: camera: isp: Enable write master for stats

In vfe 48 version the stats write masters have to be enabled
in addition to enabling the stats module. Add code to do this.
Also, the stop of write master was not programmed correctly, fix
this.

CRs-Fixed: 999619
Change-Id: Ic5b38b038508802b0b5779dc5d54ec6772f24b65
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>