DisplayModeDirector: fix a bug with DesiredDisplayModeSpecs when switching is disabled

This CL dixes a bug that left DesiredDisplayModeSpecs inconsistent
when switching was disabled.

Bug: 267008497
Test: atest FrameRateOverrideHostTest
Test: atest DisplayModeDirectorTest
Change-Id: I8277991b3adc9d686ba7c3c393162993e0e42a68