sdm: Update color modes appropriately for pluggable displays

Fix the following for pluggable displays
- Use size of SDEDisplayMode::name instead of sizeof() to get the length
  of color mode name which is a pointer.
- Update current_color_mode_ appropriately.

Change-Id: Ibe6744d15bc6e19cc2313bed6f1d3b48311f344a
Crs-fixed: 2304719
1 file changed