[SYCL][libdevice][CMake][Trivial] Fix imf-fallback missing in NVPTX (#16336)

Seems like the IMF fallback libraries are not collected in the merged
libdevice for NVPTX and AMDGPU, because the name of the CMake property
was wrong.

I don't know why our testing does not catch this. I have seen this
result in unresolved symbols earlier, but I have been sitting on this
patch for a while and did not try with current trunk.

Author: Maetveis

libdevice/cmake/modules/SYCLLibdevice.cmake

@@ -584,7 +584,7 @@ foreach(arch IN LISTS devicelib_arch)
 
     append_to_property(
       ${bc_binary_dir}/libsycl-fallback-imf-${arch}-${dtype}.${bc-suffix}
-      PROPERTY_NAME ${arch})
+      PROPERTY_NAME BC_DEVICE_LIBS_${arch})
   endforeach()
 endforeach()