sdm: Disable partial update only if is enabled.

- Request partial update disable only if it is currently enabled.
  This is to ensure that partial update does not get enabled by
  color manager even though it did not disable it.
- Fix variables initialization and assignment.

CRs-Fixed: 990583

Change-Id: Ief6b07b0361cba511b147b2aca6e246c70a8826c
1 file changed