Ensure that color_ptr gets set, and avoid color_char usage too in
that case. Fixes:
../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c: In function ‘meta_monitor_manager_kms_set_crtc_gamma’:
../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c:370:7: warning: ‘color_char’ may be used uninitialized in this function [-Wmaybe-uninitialized]
370 | g_string_append_printf (string, " %c: ", color_char);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c:351:12: note: ‘color_char’ was declared here
351 | char color_char;
| ^~~~~~~~~~
../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c:391:36: warning: ‘color_ptr’ may be used uninitialized in this function [-Wmaybe-uninitialized]
391 | (*color_ptr)[i]);
| ~^~~~~~~~~~~
../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c:350:24: note: ‘color_ptr’ was declared here
350 | unsigned short **color_ptr;
| ^~~~~~~~~
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1624>
20ac791f4b