Before this commit meta_kms_crtc_read_state was overwriting the
entire MetaKmsCrtcState struct stored in crtc->current_state including
the gamma (sub)struct.
This effectively zero-s the gamma struct each time before calling
read_gamma_state, setting the pointers where the previous gamma values
were stored to NULL without freeing the memory. Luckily this zero-ing
also sets gamma.size to 0, causing read_gamma_state to re-alloc the
arrays on each meta_kms_crtc_update_state call. But this does mean that
were leaking the old gamma arrays on each meta_kms_crtc_update_state call.
This commit fixes this by making meta_kms_crtc_read_state only overwrite
the other values in the MetaKmsCrtcState struct and leaving the gamma
sub-struct alone, this will make read_gamma_state correctly re-use the
gamma tables if the gamma table size is unchanged; or re-alloc them
(freeing the old ones) if the size has changed, fixing the memory leak.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/713
73db35c53c