CVE-2024-49893 drm/amd/display: Check stream_status before it is used

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Check streamstatus before it is used WHAT & HOW dcstategetstreamstatus can return null, and therefore null must be checked before streamstatus is used. This fixes 1 NULLRETURNS issue reported by Coverity...