drm/msm: internal property updates should update cached value

Need to update the driver-side cached value of properties when
they are updated via the internal set_property helpers,
especially for driver-generated read-only immutable properties.

Change-Id: If9a2c04d867eea41c1fa3ee2eb02964bc71afc06
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>