drm/amdgpu/display: Fix compilation issues

[Why]
Getting below build errors:
drivers/gpu/drm/amd/amdgpu/../display/dc/bios/bios_parser2.c:1419:3: error: unannotated fall-through between switch labels [-Werror,-Wimplicit-fallthrough]
                default:
                ^
drivers/gpu/drm/amd/amdgpu/../display/dc/bios/bios_parser2.c:1535:2: error: unannotated fall-through between switch labels [-Werror,-Wimplicit-fallthrough]
        default:
        ^

drivers/gpu/drm/amd/amdgpu/../display/dc/bios/bios_parser2.c:3276:20: error: variable 'v1_5' is uninitialized when used here [-Werror,-Wuninitialized]
                        for (i = 0; i < v1_5->number_of_path; ++i)
                                        ^~~~

[How]
Fix compilation issues

Signed-off-by: Chandan Vurdigere Nataraj <chandan.vurdigerenataraj@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>