Fix #5521: add @SUFFIX64@ in OpenBLASConfig.cmake.in

[Smilyf]

Fixes #5521

This PR updates OpenBLASConfig.cmake.in to correctly use the @SUFFIX64@ placeholder for CMake targets and variables.

When OpenBLAS is built with SUFFIX64=64, this ensures the exported CMake target is OpenBLAS64::OpenBLAS (instead of OpenBLAS::OpenBLAS).

To support ：

    target_link_libraries(${LIBRARY_NAME}Shared PUBLIC
        OpenBLAS64::OpenBLAS
    )

[martin-frbg]

thank you