media: dvb-core: Fix coding errors in broadcast drivers

Added Check to verify TSPP channel input source is valid.
Initialize return variables to return correct values in fail conditions.
Move deferencing of input pointer arguments after NULL checking.

CR's-Fixed: 2043689
Change-Id: I7febdb0e0f499846cfcf8836ea35c8547a5074fb
Signed-off-by: Udaya Bhaskara Reddy Mallavarapu <udaym@codeaurora.org>