msm: HDMI: Re-initialize the scan details for every HPD

After disconnecting the phone from TV which doesn't support
underscan, and connected to TV which support underscan,
underscan is not working due to non re-initialization of
scan variables. Re-initialize the underscan variables for
every HDP events.

CRs-Fixed: 375862
Change-Id: I22b7b8785ec93f9cf226e9b646a851ffb3ceff62
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>