msm: mdss: Change histogram collect error in mdp3 to EPROTO

During suspend, histogram stop will be called from control off.
However userspace would not be aware that histogram has been
disabled and will continue to send ioctl calls for collection
of histogram. This causes repeated ioctl failures, so we now
return EPROTO as the error, so that userspace is made aware
that histograms have been halted in kernel. Userspace can
make use of this return value to prevent multiple calls to
collect histogram data after histogram block was turned off.

Change-Id: I85d4d46bca3b102286b474e7126e33b03a27503a
Signed-off-by: Krishna Chaitanya Parimi <cparimi@codeaurora.org>