intel/fs: iris: Fix incorrectly emitting null-register operation when running nine-tests

Lowerings we do here can change the info. This might mess up something down the path, so gather the most recent info after all of the lowerings.

v2: Added commit with asserts that veryfy if the registers were populated.

Closes: #6946 (closed) Signed-off-by: Sviatoslav Peleshko sviatoslav.peleshko@globallogic.com