hwc2: Check color_mode_ before calling GetCurrentColorMode

Replace color_mode_->GetCurrentColorMode() call with
HWCDisplay::GetCurrentColorMode function to avoid null
pointer de-reference, since color_mode_ will not be
created for virtual display.

CRs-Fixed: 2310086
Change-Id: I4fe0ac81cddae3373a7aaa0d7dc02a911a0735fc
1 file changed