msm: mdss: Do not stop histogram from control off in mdp3

Histogram status is maintained in userspace code which is
changed with every histogram start and stop ioctl call
appropriately. Calling histogram stop from control off
results in userspace not knowing the changed histogram
collection status. Hence userspace may keep sending read
requests for histogram not knowing if collection stopped.
Removing histogram stop call from control off so that
userspace alone controls the histogram block. This is
how it was intended in MDP5 as well.

Change-Id: I3e1c26c6794512bb39b4d1ade923c6940101460c
Signed-off-by: Krishna Chaitanya Parimi <cparimi@codeaurora.org>