[ECM] Correct trusted installer logic

This was a boolean logic typo. Correct the logic by inverting it, and
use a variable to make the intention clear.

Obviously, being installed from a trusted installer should imply *more*
trustworthiness, not less.

Bug: 310655061
Test: manual
Change-Id: Ic1e0b19d5565011bc3aa0dd151b49ff0d0b2458b