drm/i915/display: take out dead code

if __waitfor timeout, ret will have -ETIMEDOUT. Then if condition
was met, and read_ret will have error that's handled.
Then if ret was zero, read_ret was zero ksv_ready must have value.

Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Link: https://lore.kernel.org/r/20250905104626.1274147-1-juhapekka.heikkila@gmail.com