msm: mdss: Do not return error on same autorefresh settings

If userspace tries to set the same autorefresh enable value as before
do not return an error, since it is not, and bail out silently.

Change-Id: If2699817dc5cb06dd8182e5125c1ae868c925ddf
Signed-off-by: Saurabh Shah <saurshah@codeaurora.org>