libhwc2.1: only replace desired mode if it has changed

There is an issue to set crtc MODE_ID property to 0 when desired mode
doesn't change. Add check to only replace desired mode if it has
changed.

Bug: 251697081
Test: fps switch, AOD in/out, screen on/off, rrs
Change-Id: I8a062e5d4396bbeb33ba0f2ff4b97d49627a4936
(cherry picked from commit 2d9696248e6c4ecc723014af39fce5aa8b0cf6d6)
Merged-In: I8a062e5d4396bbeb33ba0f2ff4b97d49627a4936