graphics/openexr: avoid _d suffix WITH_DEBUG

Apparently broken with upstream commit
https://github.com/AcademySoftwareFoundation/openexr/commit/848f84ae7504adcd89ec0da182499d5cd4e3b245

Might fix
PR: 290615
MFH: 2025Q4

No PORTREVISION bump because packaging fails if the issue strikes.