av: remove a redundant NULL check

The unconditional `readInputParameters_l` call below this condition
immediately and unconditionally dereferences `mInput`. Either
`readInputParameters_l` needs to handle a null `mInput` reasonably, or
`mInput` can never be null. This CL assumes the latter.

Bug: None
Test: TreeHugger
Change-Id: I46f89f918257f9d4aa762a03c3d03e030a17b4a9